OECD 2002
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3
FOREWORD
Several years after the Three Mile Island accident in the United States,
the Chernobyl accident in 1986 completely changed the public’s perception of
nuclear risk. While the first accident provided the impetus to develop new
research programmes on nuclear safety, the second, with its human death toll
and the dispersion of a large part of the reactor core into the environment, raised
a large number of “management” problems, not only for the treatment of
severely exposed persons, but also for the decisions that had to be taken in
respect of the population. Clearly, not only the national authorities of the Soviet
Union, but more broadly, authorities from many other affected countries were
not ready to manage an accident whose consequences were not confined to their
territory.
The way the accident was managed and the lack of information provoked
a feeling of distrust in the minds of the public that was reinforced by the fact
that radiation cannot be perceived by humans, although it can be easily
identified with electronic detectors, even at a very low level. The prospect of
contaminated food, aggravated by ambiguous, even contradictory recom-
mendations by national authorities, gave rise to a variety of reactions, and
sometimes overreactions, in the management of the accident consequences in
several European countries. In the accident country itself, where political, social
and economic conditions were worsening, the association of the Soviet regime
with nuclear activities contributed to raise feelings of mistrust towards the
public authorities.
More than sixteen years after the Chernobyl accident, public concern
remains high in spite of the considerable amount of information disseminated
by national authorities and large international organisations, the multitude of
scientific papers in the specialised press, and the numerous symposia devoted to
this accident. The same questions are still being asked and the general public,
the media and sometimes the politicians concerned, still find it difficult to
understand the information provided by the scientific community.
Public opinion in the former Soviet Union and in many other countries
affected by the accident remains convinced that certain cancers, such as those of
4
the thyroid, can only have resulted from the Chernobyl accident. This view is
partly driven by statistics showing that in European countries the incidence of
such cancers has increased. Although this cannot be attributed to the accident,
because this increase has been ongoing and was recorded long before the
accident occurred, it remains difficult for doctors to reassure patients in this
regard. As the increase in childhood thyroid cancer, which occurred primarily in
Belarus, emerged in the early 1990s, many experts were surprised by this
“early” appearance of thyroid cancer and by its geographic distribution within
the affected territories. This further aggravated public scepticism of the
scientific community.
The media have at times published pictures of human and animal
deformities without investigating their veritable connection with the accident,
and the public, struck by such images, has been allowed, unchallenged, to lay
the blame on Chernobyl. Here again, the accident has given rise to numerous
studies showing that such deformities and diseases are not linked to radiation
exposure. These conclusions, however, have not been effectively transmitted to
decision makers or the public. On the other hand, many feared a catastrophic
contamination of the River Dnieper, extending to the Mediterranean, which
never materialised. Radionuclide retention in the soil has been high, and any
remaining contamination is well below initial projections. So much the better.
In this context of public concern, the NEA has found that by far the most
consulted document on its website is the one drafted in 1996 on the impact of
the Chernobyl accident. That is why, with more recent information now
available, in particular the new United Nations Scientific Committee on the
Effects of Atomic Radiation (UNSCEAR) report published in 2000, it was
timely to update the Chernobyl: Ten Years On report. Several figures have
changed as a result of the numerous and increasingly detailed studies carried out
over the last years. The list of bibliographical references has also been updated,
with one quarter more bibliographical references than in the previous edition.
Furthermore, the NEA wished to address the questions raised by numerous
other reports that have been issued, either on the tenth anniversary of the
accident or immediately afterwards. Among these reports were those prepared
by UNSCEAR, and by the International Atomic Energy Agency (IAEA) on the
state of the environment, which had, to a large extent, served as a model for the
present report.
This report presents the knowledge gained since the accident, which has
evolved gradually. Environmental contamination, which seemed to be
decreasing fairly quickly, has reached an ecological equilibrium and, in certain
limited sectors, has even increased due to a reconcentration of
137
Cs, the only
radionuclide remaining in the different soil compartments involved in food
5
chain transfers. This process has gone as far as it can, and now, in places where
contamination persists, only the radioactive decay of caesium will reduce the
impact of the accident.
The huge effort by the international community to gain a better under-
standing of the real impact of Chernobyl continues, and should, in the next ten
years, clarify the main consequences of the accident. The main trends described
in 1996 continue to be valid in 2002: thyroid cancer in children remains the
only striking manifestation of the accident as far as the public is concerned. The
significant increase in cases of leukaemia, which had been so greatly feared, has
not, on the other hand, materialised.
Many improvements in radiation protection and emergency preparedness
have been made possible by the Chernobyl experience and we are also able to
develop a more accurate assessment of the impact of this accident. Under the
auspices of the NEA Committee on Radiation Protection and Public Health
(CRPPH), supported by other international bodies, the most outstanding
progress since the Chernobyl accident has been in learning about inter-
governmental communications and co-operation in the case of nuclear
emergencies. The International Nuclear Emergency Exercises (INEX) bear
witness to this. Governments, initially reluctant to publicly discuss nuclear
accident preparedness and management issues, now ask for such exercises to be
carried out, operators are no longer reluctant to offer their sites for this purpose,
and local authorities are pleased to invite the participants involved to appear
before the media. This shows the progress achieved in terms of communication
and involvement of all social partners. More impressive still is the progress
made concerning the distribution of stable iodine near nuclear power plants, a
subject that was more or less taboo before the accident. The NEA organised an
international colloquium on this topic, and this issue is today openly debated.
Here again, the CRPPH played an experimental and innovative role,
stressing how very important it is to involve all social partners. This idea, which
originated in the context of accident management, has been taken up by many
other disciplines, including the management of nuclear waste. This fundamental
point is also one of the positive lessons learned from the accident.
The accident was followed by numerous assistance and research
programmes supported by international organisations and bilateral agreements.
All these organisations are or will be publishing their results. This report differs
from the others in that it is a synthetic consensus view aimed at those persons
who wish to know the salient points, without having to go into the technical
details that can be found elsewhere.
6
We thank all those organisations (IAEA, UNSCEAR, FAO, WHO, EC
and others) that have provided information so that this report could be as up to
date as possible. The original report Chernobyl: Ten Years On was drafted by
Dr. Peter Waight (Canada) under the direction of an editing committee chaired
by Dr. Henri Métivier (France).
This edition was prepared by Dr. Henri Métivier on request of the
CRPPH.
7
TABLE OF CONTENTS
Foreword................................................................................................................... 3
Executive summary.................................................................................................. 9
Chapter I. The site and accident sequence ................................................... 23
The site........................................................................................... 23
The RBMK-1000 reactor .............................................................. 26
Events leading to the accident........................................................ 27
The accident ................................................................................... 28
The graphite fire............................................................................. 29
Chapter II. The release, dispersion, deposition and
behaviour of radionuclides.......................................................... 33
The source term.............................................................................. 33
Atmospheric releases................................................................ 33
Chemical and physical forms ................................................... 37
Dispersion and deposition.............................................................. 38
Within the former Soviet Union................................................ 38
Outside the former Soviet Union.............................................. 44
Behaviour of deposited radionuclides...................................... 46
Chapter III. Reactions of national authorities ................................................ 53
Within the former Soviet Union..................................................... 53
Outside the former Soviet Union ................................................... 55
More recent decisions .................................................................... 58
Chapter IV. Dose estimates .............................................................................. 61
The liquidators ............................................................................... 63
The evacuees from the 30-km zone ............................................... 65
Doses to the thyroid gland ....................................................... 66
Whole-body doses..................................................................... 66
People living in the contaminated areas......................................... 67
Doses to the thyroid gland ....................................................... 69
Whole-body doses..................................................................... 71
Populations outside the former Soviet Union ................................ 74
8
Chapter V. Health impact ............................................................................... 77
Radiation induced health effects .................................................... 78
Acute health effects................................................................... 78
Late health effects .......................................................................... 81
Thyroid cancer ......................................................................... 83
Other late health effects ........................................................... 89
Other studies .................................................................................. 90
Psychological and social health effects.......................................... 91
Within the former Soviet Union................................................ 93
Outside the former Soviet Union.............................................. 95
Chapter VI. Agricultural and environmental impacts................................... 99
Agricultural impact ........................................................................ 99
Within the former Soviet Union................................................ 100
Within Europe .......................................................................... 102
Environmental impact .................................................................... 103
Forests...................................................................................... 103
Water bodies............................................................................. 104
Sixteen years later .......................................................................... 105
Chapter VII. Potential residual risks ................................................................ 109
The Sarcophagus............................................................................ 109
Radioactive waste storage sites...................................................... 112
Chapter VIII. Shutdown of the Chernobyl plant............................................... 115
Preparation of the definitive dismantling of
the Chernobyl power plant ............................................................. 116
Storage of used fuel .................................................................. 116
Treatment of liquids effluents................................................... 117
Treatment of solid wastes......................................................... 117
The Sarcophagus............................................................................ 118
Sarcophagus database .................................................................... 119
The social consequences ................................................................ 120
Chapter IX. Lessons learned ............................................................................ 121
Operational aspects ........................................................................ 121
Scientific and technical aspects...................................................... 124
The INEX programme ................................................................... 126
Psycho-sociological programmes................................................... 128
ETHOS project ......................................................................... 128
Other studies ............................................................................ 129
Explanation of terms................................................................................................ 131
List of acronyms ....................................................................................................... 135
References ............................................................................................................. 137
9
EXECUTIVE SUMMARY
Introduction
On 26 April, 1986, the Chernobyl nuclear power station, located in
Ukraine about 20 km south of the border of Belarus, suffered a major accident
which was followed by a prolonged release to the atmosphere of large quantities
of radioactive substances. The specific features of the release favoured a
widespread distribution of radioactivity throughout the northern hemisphere,
mainly across Europe. A contributing factor was the variation of meteorological
conditions and wind regimes during the period of release. Activity transported
by the multiple plumes from Chernobyl was measured not only in Northern and
in Southern Europe, but also in Canada, Japan and the United States. Only the
Southern hemisphere remained free of contamination.
This had serious radiological, health and socio-economic consequences
for the populations of Belarus, Ukraine and Russia, which still suffer from these
consequences. Although the radiological impact of the accident in other
countries was generally very low, and even insignificant outside Europe, this
event had, however, the effect of enhancing public apprehension all over the
world on the risks associated with the use of nuclear energy.
This is one of the reasons explaining the renewed attention and effort
devoted during the last sixteen years to the reactor safety studies and to
emergency preparedness by public authorities and the nuclear industry. This
also highlights the continuing public attention to the situation at Chernobyl,
which was already significant 10 years after the accident and has not declined
6 years later. Parts of the population in some countries discuss aspects of the
accident, such as the increase in thyroid cancer, even more than before.
It now appears, therefore, the right moment to review our knowledge of
the serious aspects of the accident’s impact, to take stock of the information
accumulated and the scientific studies underway e.g. the UNSCEAR
2000 document, IAEA documents, etc; as well as to assess the degree to which
10
national authorities and experts have implemented the numerous lessons that the
Chernobyl accident taught us.
Moreover, since the last report, all units of the Chernobyl reactor have
been shut down.
This new report, prepared for the Committee on Radiation Protection and
Public Health (CRPPH) of the OECD Nuclear Energy Agency, does not differ
from the former description of the accident, but brings new data on the health
status of the population and a new view on environmental contamination.
The accident
The Unit 4 of the Chernobyl nuclear power plant was to be shutdown for
routine maintenance on 25 April 1986. On that occasion, it was decided to carry
out a test of the capability of the plant equipment to provide enough electrical
power to operate the reactor core cooling system and emergency equipment
during the transition period between a loss of main station electrical power
supply and the start up of the emergency power supply provided by diesel
engines.
Unfortunately, this test, which was considered to concern essentially the
non-nuclear part of the power plant, was carried out without a proper exchange
of information and co-ordination between the team in charge of the test and the
personnel in charge of the operation and safety of the nuclear reactor. Therefore,
inadequate safety precautions were included in the test programme and the
operating personnel were not alerted to the nuclear safety implications and
potential danger of the electrical test.
This lack of co-ordination and awareness, resulting from an insufficient
level of “safety culture” within the plant staff, led the operators to take a
number of actions which deviated from established safety procedures and led to
a potentially dangerous situation. This course of actions was compounded by
the existence of significant drawbacks in the reactor design which made the
plant potentially unstable and easily susceptible to loss of control in case of
operational errors.
The combination of these factors provoked a sudden and uncontrollable
power surge which resulted in violent explosions and almost total destruction of
the reactor. The consequences of this catastrophic event were further worsened
by the graphite moderator and other material fires that broke out in the building
11
and contributed to a widespread and prolonged release of radioactive materials
to the environment.
Dispersion and deposition of radionuclides
The release of radioactive materials to the atmosphere consisted of gases,
aerosols and finely fragmented nuclear fuel particles. This release was
extremely high in quantity, involving a large fraction of the radioactive product
inventory existing in the reactor, and its duration was unexpectedly long, over a
10-day period, with varying release rates. The duration and high altitude (about
1 km) reached by the release were largely due to the graphite fire which was
difficult to extinguish until day 10, when the releases dropped abruptly, thus
ending the period of intense release.
For these reasons and the concomitant frequent changes of wind direction
during the release period, the area affected by the radioactive plume and the
consequent deposition of radioactive substances on the ground was extremely
large, encompassing the whole Northern hemisphere, although significant
contamination outside the former Soviet Union was only experienced in part of
Europe.
The pattern of contamination on the ground and in foodchains was,
however, very uneven in some areas due to the influence of rainfall during the
passage of the plume. This irregularity in the pattern of deposition was
particularly pronounced at larger distances from the reactor site.
Since the last report we have a better view of the behaviour of
radionuclides in the contaminated areas, and we know now that the natural
decontamination processes have reached an environmental equilibrium state.
The decrease of contamination levels from now on will be mainly due to
radioactive decay indicating that radioactive cesium will be present for
approximately 300 years.
Reactions of national authorities
The scale and severity of the Chernobyl accident had not been foreseen
and took most national authorities responsible for public health and emergency
preparedness by surprise. The intervention criteria and procedures existing in
most countries were not adequate for dealing with an accident of such scale and
provided little help in decision making concerning the choice and adoption of
protective measures. In addition, early in the course of the accident there was
12
little information available and considerable political pressure, partially based
on the public perception of the radiation danger, was being exerted on the
decision makers.
In these circumstances, cautious immediate actions were felt necessary
and in many cases measures were introduced that tended to err, sometimes
excessively so, on the side of prudence rather than being driven by informed
scientific and expert judgement.
Within the territory of the former Soviet Union, short-term counter-
measures were massive and, in general, reasonably timely and effective.
However, difficulties emerged when the authorities tried to establish criteria for
the management of the contaminated areas on the long term and the associated
relocation of large groups of population. Various approaches were proposed and
criteria were applied over the years. Eventually, criteria for population resettle-
ment or relocation from contaminated areas were adopted in which radiation
protection requirements and economic compensation considerations were
intermingled. This was and continues to be a source of confusion and possible
abuse.
The progressive spread of contamination at large distances from the
accident site caused considerable concern in many countries outside the former
Soviet Union and the reactions of the national authorities to this situation were
extremely varied, ranging from a simple intensification of the normal
environmental monitoring programmes, without adoption of specific counter-
measures, to compulsory restrictions concerning the marketing and
consumption of foodstuffs.
Apart from the objective differences of contamination levels and
regulatory and public health systems between countries, one of the principal
reasons for the variety of situations observed in the different countries stems
from the different criteria adopted for the choice and application of intervention
levels for the implementation of protective actions. These discrepancies were in
some cases due to misinterpretation and misuse of international radiation
protection guidelines, especially in the case of food contamination, and were
further enhanced by the overwhelming role played in many cases by non-
radiological factors, such as socio-economic, political and psychological, in
determining the countermeasures.
This situation caused concern and confusion among the public,
perplexities among the experts and difficulties to national authorities, including
problems of public credibility, as well as a waste of efforts and unnecessary
economic losses. These problems were particularly felt in areas close to
13
international borders due to different reactions of the authorities and media in
bordering countries. However, all these issues were soon identified as an area
where several lessons should be learned and international efforts were under-
taken to harmonise criteria and approaches to emergency management.
Radiation dose estimates
Most of the population of the Northern hemisphere was exposed, to
various degrees, to radiation from the Chernobyl accident. After several years of
accumulation of dosimetric data from all available sources and dose
reconstruction calculations based on environmental contamination data and
mathematical models, it is now possible to arrive at a reasonable, although not
highly accurate, assessment of the ranges of doses received by the various
groups of population affected by the accident.
The main doses of concern are those to the thyroid in the population of
children and infants at the time of the accident, due to external irradiation and
inhalation and ingestion of radioactive iodine isotopes (
131
I and short-lived
radionuclides), and those to the whole body due to external irradiation from and
ingestion of radioactive caesium isotopes (
134
Cs and
137
Cs). According to the
most wildly accepted estimates, the situation for the different exposed groups is
the following:
• Evacuees – More than 100 000 persons were evacuated, mostly from
the 30-km radius area around the accident site, during the first few
weeks following the accident. These people received significant
doses both to the whole body and the thyroid, although the
distribution of those doses was very variable among them depending
on their positions around the accident site and the delays of their
evacuation.
Doses to the thyroid ranging from 70 millisieverts to adults up to
about 1 000 millisieverts (i.e., 1 sievert) to young children and an
average individual dose of 15 millisieverts [mSv] to the whole body
were estimated to have been absorbed by this population prior to
their evacuation. Many of these people continued to be exposed,
although to a lesser extent depending on the sites of their relocation,
after their evacuation from the 30-km zone.
• “Liquidators” – Hundreds of thousands of workers, estimated to
amount up to 600 000 and including a large number of military
personnel, were involved in the emergency actions on the site during
14
the accident and the subsequent clean-up operations which lasted for
a few years. These workers were called “liquidators”.
A restricted number, of the order of 400 people, including plant
staff, firemen and medical aid personnel, were on the site during the
accident and its immediate aftermath, and received very high doses
from a variety of sources and exposure pathways. Among them were
all those who developed acute radiation syndrome and required
emergency medical treatment. The doses to these people ranged
from a few grays to well above 10 grays to the whole body from
external irradiation and comparable or even higher internal doses, in
particular to the thyroid, from incorporation of radionuclides. A
number of scientists, who periodically performed technical actions
inside the destroyed reactor area during several years, accumulated
over time doses of similar magnitude.
The largest group of liquidators participated in clean-up operations
for variable durations over a number of years after the accident.
Although they were no longer working in emergency conditions, and
were subject to controls and dose limitations, they received
significant doses ranging from tens to hundreds of millisieverts.
• People living in contaminated areas of the former Soviet Union –
About 270 000 people continue to live in contaminated areas with
radiocaesium deposition levels in excess of 555 kilobecquerels per
square metre [kBq/m2], where protection measures still continue to
be required. Thyroid doses, due mainly to the consumption of cow’s
milk contaminated with radioiodine, were delivered during the first
few weeks after the accident; children in the Gomel region of
Belarus appear to have received the highest thyroid doses with a
range from negligible levels up to 40 sieverts, and an average of
about 1 sievert for children aged 0 to 7. Thanks to of the control of
foodstuffs in those areas, most of the radiation exposure since the
summer of 1986 is due to external irradiation from the radiocaesium
activity deposited on the ground; the whole-body doses for the
1986-89 time period are estimated to range from 5 to 250 mSv with
an average of 40 mSv.
• Populations outside the former Soviet Union – The radioactive
materials of a volatile nature (such as iodine and caesium) that were
released during the accident spread throughout the entire Northern
hemisphere. The doses received by populations outside the former
Soviet Union are relatively low, and show large differences from one
15
country to another depending mainly upon whether rainfall occurred
during the passage of the radioactive cloud. These doses range from
a lower extreme of a few microsieverts or tens of microsieverts
outside Europe, to an upper extreme of 1 or 2 mSv in some specific
areas of some European countries.
Health impact
The health impact of the Chernobyl accident can be described in terms of
acute health effects (death, severe health impairment), late health effects
(cancers) and social/accident effects that may affect health.
The acute health effects occurred among the plant personnel and the
persons who intervened in the emergency phase to fight fires, provide medical
aid and immediate clean-up operations. A total of 31 people died as a
consequence of the accident, and about 140 people suffered various degrees of
radiation sickness and radiation-related acute health impairment. No members
of the general public suffered these kinds of effects.
As far as the late health effects are concerned, namely the possible
increase of cancer incidence, since the accident there has been a real and
significant increase of carcinomas of the thyroid among the population of
infants and children exposed at the time of the accident in the contaminated
regions of the former Soviet Union. This should be attributed to the accident
until proved otherwise. There might also be some increase of thyroid cancers
among the adults living in those regions. From the observed trend of this
increase of thyroid cancers it is expected that the peak has not yet been reached
and that this kind of cancer will still continue for some time to show an excess
above its natural rate in the area.
On the other hand, the scientific and medical observation of the affected
population has not to date revealed any significant increase in other cancers,
leukaemia, congenital abnormalities, adverse pregnancy outcomes or any other
radiation induced disease that could be attributed to the Chernobyl accident.
This observation applies to the whole general population, both within and
outside the former Soviet Union. Large scientific and epidemiological research
programmes, some of them sponsored by international organisations such as the
WHO and the EC, are being conducted to provide further insight into possible
future health effects. However, the population dose estimates generally accepted
tend to predict that, with the exception of thyroid disease, it is unlikely that the
exposure would lead to discernible radiation effects in the general population
above the background of natural incidence of the same diseases. In the case of
16
the liquidators, increases in cancer have not been observed to date, but a
specific and detailed follow-up of this particular group might better reveal
increasing trends should they exist.
An important effect of the accident, which has a bearing on health, is the
appearance of a widespread status of psychological stress in the populations
affected. The severity of this phenomenon, which is mostly observed in the
contaminated regions of the former Soviet Union, appears to reflect the public
fears about the unknowns of radiation and its effects, as well as its mistrust
towards public authorities and official experts, and is certainly made worse by
the disruption of the social networks and traditional ways of life provoked by
the accident and its long-term consequences.
These accident related effects have resulted in a general degradation of
the health of the population living in the contaminated territories. Illnesses that
have been observed are not typically related to radiation exposure. Further study
of those effects should continue.
Agricultural and environmental impacts
The impact of the accident on agricultural practices, food production and
use and other aspects of the environment has been and continue to be much
more widespread than the direct health impact on humans.
Several techniques of soil treatment and decontamination to reduce the
accumulation of radioactivity in agricultural produce and cow’s milk and meat
have been tested with positive results in some cases. Nevertheless, within the
former Soviet Union, large areas of agricultural land are still excluded from use
and are expected to continue to be so for a long time. In a much larger area,
although agricultural and dairy production activities are carried out, the food
produced is subjected to strict controls and restrictions of distribution and use.
Although contamination levels showed a decreasing trend for some time
following the accident, it increasingly appears that an ecological stability has
been reached. This is particularly true in forest areas. The decrease now seems
to be following the decay period for
137
Cs, which has a 30-year half-life. Should
this trend continue, measurable contamination would be present in these areas
for approximately 10 half-lives, or 300 years.
Similar problems of control and limitation of use, although of a much
lower severity, were experienced in some countries of Europe outside the
former Soviet Union, where agricultural and farm animal production were
17
subjected to restrictions for variable durations after the accident. Most of these
restrictions were lifted some time ago. However, there are still today some areas
in Europe where restrictions on slaughter and distribution of animals are in
force. This concerns, for example, several hundreds of thousands of sheep in the
United Kingdom and large numbers of sheep and reindeer in some Nordic
countries.
The forest is a special environment where problems persist. Because of
the high filtering characteristics of trees, deposition was often higher in forests
than in other areas. An extreme case was the so-called “red forest” near to the
Chernobyl site where the irradiation was so high as to kill the trees which had to
be destroyed as radioactive waste. In more general terms, forests, being a source
of timber, wild game, berries and mushrooms as well as a place for work and
recreation, continue to be of concern in some areas and are expected to
constitute a radiological problem for a long time.
Water bodies, such as rivers, lakes and reservoirs can be, if contaminated,
an important source of human radiation exposure because of their uses for
recreation, drinking and fishing. In the case of the Chernobyl accident this
segment of the environment has not contributed significantly to the total
radiation exposure of the population. It was estimated that the component of the
individual and collective doses that can be attributed to the water bodies and
their products does not exceed 1 or 2% of the total exposure resulting from the
accident. Since the accident, it has been noted that the contamination of the
water system has not posed a public health problem during the last decade;
nevertheless, in view of the large quantities of radioactivity deposited in the
catchment area of the system of water bodies in the contaminated regions
around Chernobyl, there will continue to be for a long time a need for careful
monitoring to ensure that washout from the catchment area will not contaminate
drinking-water supplies.
Outside the former Soviet Union, no concerns were ever warranted for
the levels of radioactivity in drinking water. On the other hand, there are lakes,
particularly in Switzerland and the Nordic countries, where restrictions were
necessary for the consumption of fish. These restrictions still exist in Sweden,
for example, where thousands of lakes contain fish with a radioactivity content
which is still higher than the limits established by the authorities for sale on the
market.
18
Potential residual risks
Within seven months of the accident, the destroyed reactor was encased
in a massive concrete structure, known as the “sarcophagus”, to provide some
form of confinement of the damaged nuclear fuel and destroyed equipment and
reduce the likelihood of further releases of radioactivity to the environment.
This structure was, however, not conceived as a permanent containment but
rather as a provisional barrier pending the definition of a more radical solution
for the elimination of the destroyed reactor and the safe disposal of the highly
radioactive materials.
Years after its erection, the sarcophagus structure, although still generally
sound, raises concerns for its long-term resistance and represents a standing
potential risk. In particular, the roof of the structure presented for a long time
numerous cracks with consequent impairment of leaktightness and penetration
of large quantities of rain water which is now highly radioactive. This also
creates conditions of high humidity producing corrosion of metallic structures
which contribute to the support of the sarcophagus. Moreover, some massive
concrete structures, damaged or dislodged by the reactor explosion, are unstable
and their failure, due to further degradation or to external events, could provoke
a collapse of the roof and part of the building.
According to various analyses, a number of potential accidental scenarios
could be envisaged. They include a criticality excursion due to change of
configuration of the melted nuclear fuel masses in the presence of water leaked
from the roof, a resuspension of radioactive dusts provoked by the collapse of
the enclosure and the long-term migration of radionuclides from the enclosure
into the groundwater. The first two accident scenarios would result in the
release of radionuclides into the atmosphere which would produce a new
contamination of the surrounding area within a radius of several tens of
kilometres. It is not expected, however, that such accidents could have serious
radiological consequences at longer distances.
As far as the leaching of radionuclides from the fuel masses by the water
in the enclosure and their migration into the groundwater are concerned, this
phenomenon is expected to be very slow and it has been estimated that, for
example, it will take 45 to 90 years for certain radionuclides such as
90
Sr to
migrate underground up to the Pripyat River catchment area. The expected
radiological significance of this phenomenon is not known with certainty and a
careful monitoring of the evolving situation of the groundwater will need to be
carried out for a long time.
19
The accident recovery and clean-up operations have resulted in the
production of very large quantities of radioactive wastes and contaminated
equipment which are currently stored in about 800 sites within and outside the
30-km exclusion zone around the reactor. These wastes and equipment are
partly buried in trenches and partly conserved in containers isolated from
groundwater by clay or concrete screens. A large number of contaminated
equipment, engines and vehicles are also stored in the open air.
All these wastes are a potential source of contamination of the
groundwater which will require close monitoring until a safe disposal into an
appropriate repository is implemented.
In general, it can be concluded that the sarcophagus and the proliferation
of waste storage sites in the area constitute a series of potential sources of
release of radioactivity that threatens the surrounding area. However, any such
releases are expected to be very small in comparison with those from the
Chernobyl accident in 1986 and their consequences would be limited to a
relatively small area around the site.
In any event, initiatives have been taken internationally, and are currently
underway, to study a technical solution leading to the elimination of these
sources of residual risk on the site.
Lessons learned
The Chernobyl accident was very specific in nature and it should not be
seen as a reference accident for future emergency planning purposes. However,
it was very clear from the reactions of the public authorities in the various
countries that they were not prepared to deal with an accident of this magnitude
and that technical and/or organisational deficiencies existed in emergency
planning and preparedness in almost all countries.
The lessons that could be learned from the Chernobyl accident were,
therefore, numerous and encompassed all areas, including reactor safety and
severe accident management, intervention criteria, emergency procedures, com-
munication, medical treatment of irradiated persons, monitoring methods, radio-
ecological processes, land and agricultural management, public information, etc.
However, the most important lesson learned was probably the under-
standing that a major nuclear accident has inevitable transboundary implications
and its consequences could affect, directly or indirectly, many countries even at
large distances from the accident site. This led to an extraordinary effort to
20
expand and reinforce international co-operation in areas such as com-
munication, harmonisation of emergency management criteria and co-ordination
of protective actions. Major improvements have been achieved since the
accident, and important international mechanisms of co-operation and
information were established, such as the international conventions on early
notification and assistance in case of a radiological accident, by the IAEA and
the EC, the international nuclear emergency exercises (INEX) programme, by
the NEA, the international accident severity scale (INES), by the IAEA and
NEA and the international agreement on food contamination, by the FAO and
WHO.
At the national level, the Chernobyl accident also stimulated authorities
and experts to a radical review of their understanding of and attitude to radiation
protection and nuclear emergency issues. This prompted many countries to esta-
blish nationwide emergency plans in addition to the existing structure of local
emergency plans for individual nuclear facilities. In the scientific and technical
area, besides providing new impetus to nuclear safety research, especially on
the management of severe nuclear accidents, this new climate led to renewed
efforts to expand knowledge on the harmful effects of radiation and their
medical treatment and to revitalise radioecological research and environmental
monitoring programmes. Substantial improvements were also achieved in the
definition of criteria and methods for the information of the public, an aspect
whose importance was particularly evident during the accident and its
aftermath.
Another lesson of policy significance concerns the reclamation of
contaminated land. As has been seen, contamination, particularly in forest
environments, has tended to reach ecological stability. While it was previously
thought that contamination levels would decline due to natural removal
processes, this has not proven to be the case generally, such that policy makers
will be forced to deal with such problems for longer periods than first thought.
Because of this persistence of contamination, the importance of
stakeholder involvement in the development of approaches to living in the
contaminated territories has been highlighted. The policy lesson has been that
stakeholders, local, regional, national and international, must be involved, at the
appropriate level, in decision making processes in order to arrive at accepted
approaches to living with contamination. Such approaches need will to be long-
lasting and to evolve with changing local conditions.
21
Conclusion
The history of the modern industrial world has been affected on many
occasions by catastrophes comparable or even more severe than the Chernobyl
accident. Nevertheless, this accident, due not only to its severity but especially
to the presence of ionising radiation, had a significant impact on human society.
Not only did it produce severe health consequences and physical,
industrial and economic damage in the short term, but also its long-term
consequences, in terms of socio-economic disruption, psychological stress and
damage to the image of the nuclear energy, are expected to persist for
sometime.
However, the international community has demonstrated a remarkable
ability to apprehend and treasure the lessons drawn from this event, so that it
will be better prepared to cope with future challenges of this or another nature in
a more flexible fashion.
23
Chapter I
THE SITE AND ACCIDENT SEQUENCE
The site
At the time of the Chernobyl accident, on 26 April 1986, the Soviet
Nuclear Power Programme was based mainly upon two types of reactors, the
WWER, a pressurised light-water reactor, and the RBMK, a graphite moderated
light-water reactor. While the WWER type of reactor was exported to other
countries, the RBMK design was restricted to republics within the Soviet
Union.
The Chernobyl Power Complex, lying about 130 km north of Kiev,
Ukraine, and about 20 km south of the border with Belarus (Figure 1), consisted
of four nuclear reactors of the RBMK-1000 design, Units 1 and 2 being
constructed between 1970 and 1977, while Units 3 and 4 of the same design
were completed in 1983 (IA86). Two more RBMK reactors were under
construction at the site at the time of the accident.
To the South-east of the plant, an artificial lake of some 22 km
2
, situated
beside the river Pripyat, a tributary of the Dniepr, was constructed to provide
cooling water for the reactors.
This area of Ukraine is described as Belarussian-type woodland with a
low population density. About 3 km away from the reactor, in the new city,
Pripyat, there were 49 000 inhabitants. The old town of Chernobyl, which had a
population of 12 500, is about 15 km to the South-east of the complex. Within a
30-km radius of the power plant, the total population was between 115 000 and
135 000.
24
Figure 1. The site of the Chernobyl nuclear power complex
(modif. from IA91)
Credit: Figure IV.1 Distribution, in December 1989, of Deposited Strontium-90 Released in the
Chernobyl Accident. From: “Atlas of Caesium Deposition on Europe after the Chernobyl
Accident”. M. De Cort, G. Dubois, Sh.D. Fridman, M.G. Germenchuk, Yu.A. Izrael,
A. Janssens, A.R. Jones, G.N. Kelly, E.V. Kvasnikova, I.I. Matveenko, I.M. Nazarov,
Yu.M. Pokumeiko, V.A. Sitak, E.D. Stukin, L.Ya. Tabachny, Yu.S. Tsaturov and
S.I. Avdyushin. EUR report nr. 16733, EC, Office for Official Publications of the European
Communities, Luxembourg (1998).
25
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26
The RBMK-1000 reactor
The RBMK-1000 (Figure 2) is a Soviet designed and built graphite
moderated pressure tube type reactor, using slightly enriched (2%
235
U) uranium
dioxide fuel. It is a boiling light water reactor, with direct steam feed to the
turbines, without an intervening heat-exchanger. Water pumped to the bottom of
the fuel channels boils as it progresses up the pressure tubes, producing steam
which feeds two 500 MWe [megawatt electrical] turbines. The water acts as a
coolant and also provides the steam used to drive the turbines. The vertical
pressure tubes contain the zirconium-alloy clad uranium-dioxide fuel around
which the cooling water flows. A specially designed refuelling machine allows
fuel bundles to be changed without shutting down the reactor.
The moderator, whose function is to slow down neutrons to make them
more efficient in producing fission in the fuel, is constructed of graphite. A
mixture of nitrogen and helium is circulated between the graphite blocks largely
to prevent oxidation of the graphite and to improve the transmission of the heat
produced by neutron interactions in the graphite, from the moderator to the fuel
channel. The core itself is about 7 m high and about 12 m in diameter. There are
four main coolant circulating pumps, one of which is always on standby. The
reactivity or power of the reactor is controlled by raising or lowering
211 control rods, which, when lowered, absorb neutrons and reduce the fission
rate. The power output of this reactor is 3 200 MWt (megawatt thermal) or
1 000 MWe, although there is a larger version producing 1 500 MWe. Various
safety systems, such as an emergency core cooling system and the requirement
for an absolute minimal insertion of 30 control rods, were incorporated into the
reactor design and operation.
The most important characteristic of the RBMK reactor is that it
possesses a “positive void coefficient”. This means that if the power increases
or the flow of water decreases, there is increased steam production in the fuel
channels, so that the neutrons that would have been absorbed by the denser
water will now produce increased fission in the fuel. However, as the power
increases, so does the temperature of the fuel, and this has the effect of reducing
the neutron flux (negative fuel coefficient). The net effect of these two opposing
characteristics varies with the power level. At the high power level of normal
operation, the temperature effect predominates, so that power excursions
leading to excessive overheating of the fuel do not occur. However, at a lower
power output of less than 20% the maximum, the positive void coefficient effect
is dominant and the reactor becomes unstable and prone to sudden power
surges. This was a major factor in the development of the accident.
27
Events leading to the accident (IA86, IA86a)
The Unit 4 reactor was to be shutdown for routine maintenance on
25 April 1986. It was decided to take advantage of this shutdown to determine
whether, in the event of a loss of station power, the slowing turbine could
provide enough electrical power to operate the emergency equipment and the
core cooling water circulating pumps, until the diesel emergency power supply
became operative. The aim of this test was to determine whether cooling of the
core could continue to be ensured in the event of a loss of power.
This type of test had been run during a previous shut-down period, but
the results had been inconclusive, so it was decided to repeat it. Unfortunately,
this test, which was considered essentially to concern the non-nuclear part of the
power plant, was carried out without a proper exchange of information and co-
ordination between the team in charge of the test and the personnel in charge of
the operation and safety of the nuclear reactor. Therefore, inadequate safety
precautions were included in the test programme and the operating personnel
were not alerted to the nuclear safety implications of the electrical test and its
potential danger.
The planned programme called for shutting off the reactor’s emergency
core cooling system (ECCS), which provides water for cooling the core in an
emergency. Although subsequent events were not greatly affected by this, the
exclusion of this system for the whole duration of the test reflected a lax attitude
towards the implementation of safety procedures.
As the shutdown proceeded, the reactor was operating at about half
power when the electrical load dispatcher refused to allow further shutdown, as
the power was needed for the grid. In accordance with the planned test
programme, about an hour later the ECCS was switched off while the reactor
continued to operate at half power. It was not until about 23:00 hr on 25 April
that the grid controller agreed to a further reduction in power.
For this test, the reactor should have been stabilised at about 1 000 MWt
prior to shut down, but due to operational error the power fell to about 30 MWt,
where the positive void coefficient became dominant. The operators then tried
to raise the power to 700-1 000 MWt by switching off the automatic regulators
and freeing all the control rods manually. It was only at about 01:00 hr on
26 April that the reactor was stabilised at about 200 MWt.
Although there was a standard operating order that a minimum of
30 control rods was necessary to retain reactor control, in the test only
6-8 control rods were actually used. Many of the control rods were withdrawn
28
to compensate for the build up of xenon which acted as an absorber of neutrons
and reduced power. This meant that if there were a power surge, about
20 seconds would be required to lower the control rods and shut the reactor
down. In spite of this, it was decided to continue the test programme.
There was an increase in coolant flow and a resulting drop in steam
pressure. The automatic trip which would have shut down the reactor when the
steam pressure was low, had been circumvented. In order to maintain power the
operators had to withdraw nearly all the remaining control rods. The reactor
became very unstable and the operators had to make adjustments every few
seconds trying to maintain constant power.
At about this time, the operators reduced the flow of feedwater,
presumably to maintain the steam pressure. Simultaneously, the pumps that
were powered by the slowing turbine were providing less cooling water to the
reactor. The loss of cooling water exaggerated the unstable condition of the
reactor by increasing steam production in the cooling channels (positive void
coefficient), and the operators could not prevent an overwhelming power surge,
estimated to be 100 times the nominal power output.
The sudden increase in heat production ruptured part of the fuel and small
hot fuel particles, reacting with water, caused a steam explosion, which
destroyed the reactor core. A second explosion added to the destruction two to
three seconds later. While it is not known for certain what caused the
explosions, it is postulated that the first was a steam/hot fuel explosion, and that
hydrogen may have played a role in the second.
Some medias had reported a sismic origin of the accident, however the
scientific credibility of the paper at the origin of this rumour (St98) has been
discarded.
The accident
The accident occurred at 01:23 hr on Saturday, 26 April 1986, when the
two explosions destroyed the core of Unit 4 and the roof of the reactor building.
In the IAEA Post-Accident Assessment Meeting in August 1986 (IA86),
much was made of the operators’ responsibility for the accident, and not much
emphasis was placed on the design faults of the reactor. Later assessments
(IA86a, UN00) suggest that the event was due to a combination of the two, with
a little more emphasis on the design deficiencies and a little less on the operator
actions.
29
The two explosions sent fuel, core components and structural items and
produced a shower of hot and highly radioactive debris, including fuel, core
components, structural items and graphite into the air and exposed the destroyed
core to the atmosphere. The plume of smoke, radioactive fission products and
debris from the core and the building rose up to about 1 km into the air. The
heavier debris in the plume was deposited close to the site, but lighter
components, including fission products and virtually all of the noble gas
inventory were blown by the prevailing wind to the North-west of the plant.
Fires started in what remained of the Unit 4 building, giving rise to
clouds of steam and dust, and fires also broke out on the adjacent turbine hall
roof and in various stores of diesel fuel and inflammable materials. Over
100 fire-fighters from the site and called in from Pripyat were needed, and it
was this group that received the highest radiation exposures and suffered the
greatest losses in personnel. A first group of 14 firemen arrived on the scene of
the accident at 1.28 a.m. Reinforcements were brought in until about 4 a.m.,
when 250 firemen were available and 69 firemen participated in fire control
activities. By 2.10 a.m., the largest fires on the roof of the machine hall had
been put out, while by 2.30 a.m., the largest fires on the roof of the reactor hall
were under control. These fires were put out by 05:00 hr of the same day, but by
then the graphite fire had started. Many firemen added to their considerable
doses by staying on call on site. The intense graphite fire was responsible for
the dispersion of radionuclides and fission fragments high into the atmosphere.
The emissions continued for about twenty days, but were much lower after the
tenth day when the graphite fire was finally extinguished.
The graphite fire
While the conventional fires at the site posed no special firefighting
problems, very high radiation doses were incurred by the firemen, resulting in
31 deaths. However, the graphite moderator fire was a special problem. Very
little national or international expertise on fighting graphite fires existed, and
there was a very real fear that any attempt to put it out might well result in
further dispersion of radionuclides, perhaps by steam production, or it might
even provoke a criticality excursion in the nuclear fuel.
A decision was made to layer the graphite fire with large amounts of
different materials, each one designed to combat a different feature of the fire
and the radioactive release. The first measures taken to control fire and the
radionuclides releases consisted of dumping neutron-absorbing compounds and
fire-control material into the crater that resulted from the destruction of the
reactor. The total amount of materials dumped on the reactor was about 5 000 t
30
including about 40 t of borons compounds, 2 400 t of lead, 1 800 t of sand and
clay, and 600 t of dolomite, as well as sodium phosphate and polymer liquids
(Bu93). About 150 t of material were dumped on 27 April, followed by 300 t on
28 April, 750 t on 29 April, 1 500 t on 30 April, 1 900 t on 1 May and 400 t on
2 May. About 1 800 helicopter flights were carried out to dump materials onto
the reactor; During the first flights, the helicopter remained stationary over the
reactor while dumping materials. As the dose rates received by the helicopter
pilots during this procedure were too high, it was decide that the materials
should be dumped while the helicopters travelled over the reactor. This
procedure caused additional destruction of the standing structures and spread
the contamination. Boron carbide was dumped in large quantities from
helicopters to act as a neutron absorber and prevent any renewed chain reaction.
Dolomite was also added to act as heat sink and a source of carbon dioxide to
smother the fire. Lead was included as a radiation absorber, as well as sand and
clay which it was hoped would prevent the release of particulates. While it was
later discovered that many of these compounds were not actually dropped on the
target, they may have acted as thermal insulators and precipitated an increase in
the temperature of the damaged core leading to a further release of
radionuclides a week later.
The further sequence of events is still speculative, although elucidated
with the observation of residual damage to the reactor (Si94, Si04a, Si94b). It is
suggested that the melted core materials settled to the bottom of the core shaft,
with the fuel forming a metallic layer below the graphite. The graphite layer had
a filtering effect on the release of volatile compounds. But after burning without
the filtering effect of an upper graphite layer, the release of volatile fissions
products from the fuel may have increased, except for non-volatile fission
products and actinides, because of reduced particulate emission. On day 8 after
the accident, the corium melted through the lower biological shield and flowed
onto the floor. This redistribution of corium would have enhanced the
radionuclide releases, and on contact with water corium produced steam,
causing an increase of radionuclieds at the last stage of the active period.
By May 9, the graphite fire had been extinguished, and work began on a
massive reinforced concrete slab with a built-in cooling system beneath the
reactor. This involved digging a tunnel from underneath Unit 3. About four
hundred people worked on this tunnel which was completed in 15 days,allowing
the installation of the concrete slab. This slab would not only be of use to cool
the core if necessary, it would also act as a barrier to prevent penetration of
melted radioactive material into the groundwater.
31
In summary
The Chernobyl accident was the product of a lack of “safety culture”. The
reactor design was poor from the point of view of safety and unforgiving for the
operators, both of which provoked a dangerous operating state. The operators
were not informed of this and were not aware that the test performed could have
brought the reactor into an explosive condition. In addition, they did not comply
with established operational procedures. The combination of these factors
provoked a nuclear accident of maximum severity in which the reactor was
totally destroyed within a few seconds.
33
Chapter II
THE RELEASE, DISPERSION, DEPOSITION AND
BEHAVIOUR OF RADIONUCLIDES
The source term
The “source term” is a technical expression used to describe the
accidental release of radioactive material from a nuclear facility to the
environment. Not only are the levels of radioactivity released important, but
also their distribution in time as well as their chemical and physical forms. The
initial estimation of the Source Term was based on air sampling and the
integration of the assessed ground deposition within the then Soviet Union. This
was clear at the IAEA Post-Accident Review Meeting in August 1986 (IA86),
when the Soviet scientists made their presentation, but during the discussions it
was suggested that the total release estimate would be significantly higher if the
deposition outside the Soviet Union territory were included. Subsequent
assessments support this view, certainly for the caesium radionuclides (Wa87,
Ca87, Gu89). The initial estimates were presented as a fraction of the core
inventory for the important radionuclides and also as total activity released.
Atmospheric releases
In the initial assessment of releases made by the Soviet scientists and
presented at the IAEA Post-Accident Assessment Meeting in Vienna (IA86), it
was estimated that 100% of the core inventory of the noble gases (xenon and
krypton) was released, and between 10 and 20% of the more volatile elements
of iodine, tellurium and caesium. The early estimate for fuel material released to
the environment was 3 ± 1.5% (IA86). This estimate was later revised to
3.5 ± 0.5% (Be91). This corresponds to the emission of 6 t of fragmented fuel.
The IAEA International Nuclear Safety Advisory Group (INSAG) issued
in 1986 its summary report (IA86a) based on the information presented by the
Soviet scientists to the Post-Accident Review Meeting. At that time, it was
34
estimated that 1 to 2 exabecquerels (EBq) were released. This did not include
the noble gases, and had an estimated error of ±50%. These estimates of the
source term were based solely on the estimated deposition of radionuclides on
the territory of the Soviet Union, and could not take into account deposition in
Europe and elsewhere, as the data were not then available.
However, more deposition data (Be90) were available when, in their
1988 Report (UN88), the United Nations Scientific Committee on the Effects of
Atomic Radiation (UNSCEAR) gave release figures based not only on the
Soviet data, but also on worldwide deposition. The total
137
Cs release was
estimated to be 70 petabecquerels (PBq) of which 31 PBq were deposited in the
Soviet Union.
Later analyses carried out on the core debris and the deposited material
within the reactor building have provided an independent assessment of the
environmental release. These studies estimate that the release fraction of
137
Cs
was 20 to 40% (85 ± 26 PBq) based on an average release fraction from fuel of
47% with subsequent retention of the remainder within the reactor building
(Be91). After an extensive review of the many reports (IA86, Bu93), this was
confirmed. For
131
I, the most accurate estimate was felt to be 50 to 60% of the
core inventory of 3 200 PBq. The current estimate of the source term (De95) is
summarised in Table 1.
From the radiological point of view,
131
I and
137
Cs are the most important
radionuclides to consider, because they are responsible for most the radiation
exposure received by the general population.
The release pattern over time is well illustrated in Figure 3 (Bu93). The
initial large release was principally due to the mechanical fragmentation of the
fuel during the explosion. It contained mainly the more volatile radionuclides
such as noble gases, iodines and some caesium. The second large release
between day 7 and day 10 was associated with the high temperatures reached in
the core melt. The sharp drop in releases after ten days may have been due to a
rapid cooling of the fuel as the core debris melted through the lower shield and
interacted with other material in the reactor. Although further releases probably
occurred after 6 May, these are not thought to have been large.
35
Table 1. Current estimate of radionuclide releases
during the Chernobyl accident (modif. from
95
De)
Core inventory
on 26 April 1986
Total release during
the accident
Nuclide Half-life Activity
(PBq)
Percent of
inventory
Activity
(PBq)
33
Xe
131
I
134
Cs
137
Cs
132
Te
89
Sr
90
Sr
140
Ba
95
Zr
99
Mo
103
Ru
106
Ru
141
Ce
144
Ce
239
Np
238
Pu
239
Pu
240
Pu
241
Pu
242
Cm
5.3 d
8.0 d
2.0 y
30.0 y
78.0 h
52.0 d
28.0 y
12.8 d
65.0 d
67.0 h
39.6 d
1.0 y
33.0 d
285.0 d
2.4 d
86.0 y
24 400.0 y
6 580.0 y
13.2 y
163.0 d
6 500
3 200
180
280
2 700
2 300
200
4 800
5 600
4 800
4 800
2 100
5 600
3 300
27 000
1
0.85
1.2
170
26
100
50-60
20-40
20-40
25-60
4-6
4-6
4-6
3.5
>3.5
>3.5
>3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
3.5
6500
~1760
~54
~85
~1150
~115
~10
~240
196
>168
>168
>73
196
~116
~95
0.035
0.03
0.042
~6
~0.9
Fifteen years on, the estimation made in 1996 is still valid. However the
results presented in Table 1 are incomplete with respect to the release of the
short-lived radionuclides (
132
I and
135
I). In the UNSCEAR 2000 report (UN00),
the overall releases of short-lived radioiodines are presented on the basis of
early and re-estimated informations (Ab86, Iz90); they are found to be
substantially lower than those of
131
I (1760 PBq), 1040 PBq, 910, 25 and 250
respectively for
132
I,
133
I,
134
I and
135
I,
132
I is assumed to be in radioactive
equilibrium with
132
Te.
36
Figure 3. Daily release rate of radioactive substances
into the atmosphere (modif. from IA86a)
0.75
0.65
0.60
0.55
0.50
0.45
0.40
0.30
0.25
0.20
0.15
0.10
1 2 3 4 5 6 8 9 10 11 7
0.05
0.00
0.35
0.70
Days after initiation of the accident on 26 April
R
e
l
e
a
s
e

r
a
t
e

(
E
B
q
/
d
a
y
)
+ 50% error bars _
37
The estimated daily releases of
131
I during the accident is given in
Table 2.
Table 2. Daily releases of
131
I
Day of release Daily releases (PBq)
26 April 704
27 April 204
28 April 150
29 April 102
30 April 69
1 May 62
2 May 102
3 May 107
4 May 130
5 May 130
Total 1760
Although the releases were considerably reduced on 5 and 6 May (days 9
and 10) after the accident), continuing low-level releases occurred in the
following week and for up to 40 days after the accident, particularly on 15 and
16 may, attributable to continuing outbreaks of fires or to hot areas in the
reactor. These later releases can be correlated with increased concentrations of
radionuclides in air measured at Kiev and Vilnius.
Chemical and physical forms
The release of radioactive material to the atmosphere consisted of gases,
aerosols and finely fragmented fuel. Gaseous elements, such as krypton and
xenon escaped more or less completely from the fuel material. In addition to its
gaseous and particulate form, organically bound iodine was also detected. The
ratios between the various iodine compounds varied with time. As mentioned
above, 50 to 60% of the core inventory of iodine was thought to have been
released in one form or another. Other volatile elements and compounds, such
as those of caesium and tellurium, attached to aerosols, were transported in the
air separate from fuel particles. There were only a few measurements of the
38
aero-dynamic size of the radioactive particle releases during the first days of the
accident. The activity distribution of the particle size was found to be well
represented as the superposition of two log-normal functions, one with an
activity median aerodynamic diameter (AMAD) ranging from 0.3 to 1.5 P and
another with an AMAD of 10 P. The larger particles contained about 80-90%
of the activity of non-volatile radionuclides such as
95
Zr,
95
Nb,
140
La,
144
Ce and
transuranium elements embedded in the uranium matrix of the fuel.
Unexpected features of the source term, due largely to the graphite fire,
were the extensive releases of fuel material and the long duration of the release.
Elements of low volatility, such as cerium, zirconium, the actinides and to a
large extent barium, lanthanum and strontium also, were embedded in fuel
particles. Larger fuel particles were deposited close to the accident site, whereas
smaller particles were more widely dispersed. Other condensates from the
vaporised fuel, such as radioactive ruthenium, formed metallic particles. These,
as well as the small fuel particles, were often referred to as “hot particles”, and
were found at large distances from the accident site (De95). Typical activities
per hot-particles are 0.1-1 kBq for fuel fragments and 0.5-10 kBq for ruthenium
particles, the diameters being about 10 P WR EH FRPSDUHG ZLWK VL]HV RI
0.4-0.7 P IRU WKH SDUWLFOHV DVVRFLDWHG ZLWK WKH DFWLYLWLHV RI
131
I and
137
Cs
(De88, De91).
Dispersion and deposition
Radioactive contamination of the ground was found to some extend in
practically every country of the northern hemisphere. European commission
published on the basis of local measurements an atlas of contamination in
Europe (De98).
Within the former Soviet Union
During the first 10 days of the accident when important releases of
radioactivity occurred, meteorological conditions changed frequently, causing
significant variations in release direction and dispersion parameters. Deposition
patterns of radioactive particles depended highly on the dispersion parameters,
the particle sizes, and the occurrence of rainfall. The largest particles, which
were primarily fuel particles, were deposited essentially by sedimentation
within 100 km of the reactor. Small particles were carried by the wind to large
distances and were deposited primarily with rainfall. The radionuclide
composition of the release and of the subsequent deposition on the ground also
varied considerably during the accident due to variations in temperature and
other parameters during the release.
137
Cs was selected to characterise the
39
magnitude of the ground deposition because (1) it is easily measurable, and (2)
it was the main contributor to the radiation doses received by the population
once the short-lived
131
I had decayed. However, during the first weeks after the
accident, most of the activity deposited on the ground consisted of short-lived
radionuclides, of which
131
I was the most important radiologically. All the maps
established in the former Soviet Union were mainly based on the limited
number of measurement of
131
I, and they use
137
Cs measurements as a guide.
These maps must be regarded with caution, as the ratio of
131
I to
137
Cs
deposition densities was found to vary over a large range in Belarus, 5 to 10,
this ratio has been not seriously studied in many countries.
The three main spots of contamination resulting from the Chernobyl
accident have been called the Central, Bryansk-Belarus, and Kaluga-Tula-Orel
spots (Figure 4, pages 49-50). The Central spot was formed during the initial,
active stage of the release predominantly to the West and North-west (Figure 5,
pages 51-52). Ground depositions of
137
Cs of over 40 kilobecquerels per square
metre [kBq/m
2
] covered large areas of the Northern part of Ukraine and of the
Southern part of Belarus. The most highly contaminated area was the 30-km
zone surrounding the reactor, where
137
Cs ground depositions generally
exceeded 1 500 kBq/m
2
(Ba93).
Areas of high contamination of
137
Cs occurred thoughout the far zone,
depending primarly on rainfall at the time the plume passed over. The Bryansk-
Belarus spot, centered 200 km to the North-northeast of the reactor, was formed
on 28-29 April as a result of rainfall on the interface of the Bryansk region of
Russia and the Gomel and Mogilev regions of Belarus. The ground depositions
of
137
Cs in the most highly contaminated areas in this spot were comparable to
the levels in the Central spot and reached 5 000 kBq/m
2
in some villages
(Ba93).
The Kaluga-Tula-Orel spot in Russia, centered approximately 500 km
North-east of the reactor, was formed from the same radioactive cloud that
produced the Bryansk-Belarus spot, as a result of rainfall on 28-29 April.
However, the levels of deposition of
137
Cs were lower, usually less than
600 kBq/m
2
(Ba93).
In addition, outside the three main hot spots in the greater part of the
European territory of the former Soviet Union, there were many areas of
radioactive contamination with
137
Cs levels in the range 40 to 200 kBq/m
2
.
Overall, the territory of the former Soviet Union initially contained
approximately 3 100 km
2
contaminated by
137
Cs with deposition levels
exceeding 1 500 kBq/m
2
; 7 200 km
2
with levels of 600 to 1 500 kBq/m
2
; and
103 000 km
2
with levels of 40 to 200 kBq/m
2
(US91).
Figure 4. Deposition of Caesium-137 in Belarus*
* From: ATLAS of Caesium Deposition on Europe after
the Chernobyl Accident
M. De Cort, G. Dubois, Sh. D. Fridman,
M.G. Germenchuk, Yu A. Izrael, A. Janssens,
A.R. Jones, G.N. Kelly, E.V. Kvasnikova,
I.I. Matveenko, I.M. Nazarov, Yu M. Pokumeiko,
V.A. Sitak, E.D. Stukin, L. Ya. Tabachny,
Yu. S. Tsaturov and S.I. Avdyushin
EUR report nr. 16733, EC, Office for Official
Publications of the European Communities,
Luxembourg (1998).
Figure 5. Deposition of Caesium-137 in Ukraine*
* From: ATLAS of Caesium Deposition on Europe after
the Chernobyl Accident
De Cort, G. Dubois, SH. D. Fridman,
M.G. Germenchuk, Yu A. Izrael, A. Janssens,
A.R. Jones, G.N. Kelly, E.V. Kvasnikova,
I.I. Matveenko, I.M. Nazarov, Yu. S. Tsaturov and
S.I. Avdyushin
EUR report nr. 16733, EC, Office for Official
Publications of the European Communities,
Luxembourg (1998).
44
The principal physico-chemical form of the deposited radionuclides are:
dispersed fuel particles, condensation-generated particles, and mixed-type
particles. The distribution in the nearby contaminated zone (<100km) reflected
the radionuclide composition of the fuel and differs from that in the far zone
(>100km to 2 000 km). Large particles, deposited in the near zone, contained
fuel (U, Pu) refractory elements (Zr, Mo, Ce and Np) and intermediate elements
(Ru, Ba, Sr). The volatile elements (I, Te and Cs) in the form of condensation-
generated particles, were more widely disperded in the far zone.
Deposition of
90
Sr was mostly in the near zone of the accident as for
239
Pu; the only area with plutonium exceeding 4 kBq m
-2
was located within the
30-km zone, in the Gomel-Mogilev-Briansk area. (De98)
Outside the former Soviet Union
Radioactivity was first detected outside the Soviet Union at a Nuclear
Power station in Sweden, where monitored workers were noted to be
contaminated. It was at first believed that the contamination was from a
Swedish reactor. When it became apparent that the Chernobyl reactor was the
source, monitoring stations all over the world began intensive sampling
programmes.
The radioactive plume was tracked as it moved over the European part of
the Soviet Union and Europe (Figure 6). Initially the wind was blowing in a
Northwesterly direction and was responsible for much of the deposition in
Scandinavia, the Netherlands and Belgium and Great Britain. Later the plume
shifted to the South and much of Central Europe, as well as the Northern Medi-
terranean and the Balkans, received some deposition, the actual severity of
which depended on the height of the plume, wind speed and direction, terrain
features and the amount of rainfall that occurred during the passage of the
plume.
Most countries in Europe experienced some deposition of radionuclides,
mainly
137
Cs and
134
Cs, as the plume passed over the country. In Austria,
Eastern and Southern Switzerland, parts of Southern Germany and Scandinavia,
where the passage of the plume coincided with rainfall, the total deposition
from the Chernobyl release was greater (exceeding 37 kBq m
-2
, with an
extensive deposition in a 2-4 km
2
area in Sweden within the commune of Gävle
(exceeding 185 kBq m
-2
) (Ed91) than that experienced by most other countries,
whereas Spain, France and Portugal experienced the least deposition. For
example, the estimated average depositions of
137
Cs in the provinces of Upper
Austria, Salzburg and Carinthia in Austria were 59, 46 and 33 kBq/m
2
45
Figure 6. Areas covered by the main body of the radioactive cloud on
various days during the release
Credit: ARAC
2
6

A
p
r
i
l

1
9
8
6
2
8

A
p
r
i
l

1
9
8
6
3
0

A
p
r
i
l

1
9
8
6
0
2

M
a
y

1
9
8
6
0
4

M
a
y

1
9
8
6
0
6

M
a
y

1
9
8
6
46
respectively, whereas the average
137
Cs deposition in Portugal was 0.02 kBq/m
2
(Un88). It was reported that considerable secondary contamination occurred due
to resuspension of material from contaminated forest. This was not confirmed
by later studies.
While the plume was detectable in the Northern hemisphere as far away
as Japan and North America, countries outside Europe received very little
deposition of radionuclides from the accident. No deposition was detected in the
Southern hemisphere by the surveillance networks of environmental radiation
(Un88).
Behaviour of deposited radionuclides
The environmental behaviour of deposited radionuclides depends on the
physical and chemical characteristics of the radionuclides and on the type of
fallout, dry or wet, the size and shape of particles and the environment. For
example, particles produced by gas-to-particle conversion through chemical
reactions, nucleation and condensation as well as coagulation have a large
specific surface and are generally more soluble than explosion generated
particles, such as large fuel particles particles generated by mechanical
processes like explosion of fuel.
For short-lived radionuclides, such as iodine isotopes, the main pathway
of exposure of humans is the transfer of the amount deposited on leafy
vegetables that are consumed within a few days, or on pasture grass that is
grazed on by cows or goats, giving rise to the contamination of milk. Long term
behaviour is not relevant, because
131
I has a physical half-life of only 8 days.
Radionuclides deposited on soil migrate downwards and reach the part of
soil containing roots, and the time of residence in this area would partly
determinate migration to vegetation. Observations strongly suggest that the
migration profiles are established very early after contamination under the
influence of the early conditions prevailing immediately after contamination,
such as soil moisture and first rain events, which may be the paramount in
determining the extent to which radionuclides will penetrate in depth (Br00).
The vertical migration of
137
Cs and
90
Sr in soil of different type of meadows has
been rather slow, and the greater fraction of radionuclides is still contained in
the upper soil layers (0-10 cm). The effective half-time of clearance from root
layer has been estimated to range from 10 to 25 years for
137
Cs. Early after the
accident the transfer coefficients of
137
Cs to plant decreased by 1.5 to 7 times
but later from the observed persisting mobility of radiocaesium, and particularly
the increase in effective ecological half lives tending towards the physical decay
47
rate of
137
Cs, it now seems that the sorption-desorption process of radiocaesium
in soils and sediments is tending towards a reversible steady-state and the
practical consequences for plant contamination in the environment is that
foodstuffs will remain contaminated for much longer than initially expected
(Sm00).
The contribution of aquatic pathways to the dietary intake of
137
Cs and
90
Sr is usually quite small, However the relative importance, in comparison to
terrestrial pathways, may be high in some lakes of Scandinavia and in Russia. In
mountains we can observe by run-off some reconcentrations of the radioactivity
in lower areas and for example in the South part of the French alps the
137
Cs
contamination was in 1992 about 20 000 Bq.m
-3
, corresponding to an activity of
1 760 Bq.kg
-1
in soil samples. In some specific, small areas, (only a fraction of a
square meter) hot spots have been measured at 55 800 Bq.kg
-1
in 1992,
314 000 Bq.kg
-1
in 1995, and500 000 Bq.m
-2
in 2000. These hot spots are the
consequences of the runoff of melting water coming from snow which fell after
the 1986 contamination of the upper part of the mountain. These hot spots have
been found in small basins lower in the forest or under larchs where snow
accumulates. However these hot spots being of small surface (cm
2
to m
2
) are
offwalking tracks, pose little risk of irradiation for hikers. For example, it has
been estimated that a hiker would receive about 0.001 mSv during a 4 hour rest
in the vicinity of such a hot-spot. (Ma 97). These hot-spots will remain active
for several decades, their decay following the physical half-life of
137
Cs.
Drinking water in the affected areas is weakly contaminated, less than
1Bq of
137
Cs or
90
Sr per litre. The mean annual activity of
137
Cs in the water of
Pripiat river and in the Kiev reservoirs has now stabilised within a range of
from 1 to 0.2 Bq.l
-1
(Bq per litre), ten time higher than the values obtained
before the 1986 accident. The
90
Sr activity of the Pripiat river is sometimes
higher than authorised levels for drinking water (2 Bq.l
-1
) due to meteorological
conditions, rains and floods.
From 26 April to 6 March 1986, during the period of releases, the highest
levels of radioactivity measured in water of the Pripiat river was of the order of
100 000 Bq/l, principally from
131
I. The activity in the Pripiat declined to around
a few thousand Bq/l by mid-May 1986, and to 200 Bq/l in June 1986. From the
end of November 1986 to the beginning of 1987, the activity in the Pripiat was
rarely measured above 40 Bq/l. From 1987 on,
137
Cs and
90
Sr were the only
radionuclides measured in significant quantities. Since 1988,
90
Sr is the
radioelement of highest concentration in the waters of the Pripiat.
The chemical form of the
137
Cs that was deposited is fairly insoluable,
and is not quickly extracted from soil by surface runoff water. Most of the
137
Cs
48
transferred to the Pripiat river by runoff water came from the 30 km exclusion
zone. As a result of this low solubility, only 1 to 5% of the initial
137
Cs activity
reached the Black Sea, the rest accumulating in various reservoirs of the Dniepr,
of which more than half stayed in the Kiev reservoir.
The activity of
90
Sr in Pripiat river water is a few times higher than the
level authorised for human consumption, 2 Bq/l. During flooding in the fall of
1988,
90
Sr activity reached 9.6 Bq/l. As a result of significant blockage of water
during particularly high flooding,
90
Sr concentrations reached 12.2 Bq/l in
January 1991, and 5.9 Bq/l in February 1994.
In 1986, during the accident and the following months, the
137
Cs activity
released into the Dniepr was estimated to be 66 TBq. Subsequently, leaching
from soils by surface water and floods resulted in a measurable increase of
radionuclide concentrations in the Pripiat river. The following Table 3 indicates
the respective influxes of
137
Cs and
90
Sr in the Pripiat between 1986 and 1998,
as well as the resulting water concentrations.
The cities of Kiev, Kremenchug et Kahovsk are partly fed by Dniepr
reservoirs (see Figure 7). The table shows the annual average levels of
137
Cs and
90
Sr in the Pripiat river from 1986 to 1998 (Po01), but it could be observed
peaks of activity ten time higher during floods.
Graphs in the Figure 7 show the evolution of
137
Cs and
90
Sr
concentrations in these reservoirs from 1986 to 1998.
It has been shown that forests can deliver large radiation doses through
the consumption of berries, mushrooms and game, but also through the
industrial use of forest products. Radiological consequences result from energy
production using radioactively contaminated biofuels from forests in the north
of Europe and use of waste products or ashes and their recycling back to the
forest as fertilizer.
On the forest podzolic soils, migration of
137
Cs is pronounced, with
increased amounts in the mineral layers ten years after aerial distribution. More
than a decade after Chernobyl accident, the total inventory is still rising in pine
trees of boreal forests. There is almost no
137
Cs loss via runoff water from
boreal forest ecosystems except from the wetter portions of bogs.
49
Figure 7. Possible groundwater flow directions in the Dniepr basin
137
Cs and
90
Sr concentrations in Bq/L-1, in the reservoirs of Kiev, Kremenchug
and Kahkovka. Black area reresent activities entering in the reservoirs, white
areas activities leaving reservoirs (From Po01)
CRIMEA
UKRAINE
BELARUS
ODESSA
BLACK SEA
NIKOLAYEV
KHERSON
KACHOVKA
NIKOPOL
DNEPRODZERZHINSK
KREMENCHUG CHERKASSY
SUMY
CHERNIGOV
CHERNOBYL
ZHITOMIR
KIEV
ZAPOROZHE
DNEPROPETROVSK
res. of KIEV
res. of KANEV
res. of KREMENCHUG
res.of DNEPROZERZHINSK
res. of KACHOVKA
res. of DNEPROPETROVSK
Possible directions of
underground water flows
100 km
D
n
ie
p
r
P
r
ip
y
a
t
D
e
s
n
a
Liz
Teterev
Z
o
w
y
th
Irp
e
n
Dniepr
Credit: “Catastrophes et accidents nucléaires dans l’ex-union soviétique”, D. Robeau.
50
Table 3. Evolution of average radioactivity in the Pripiat river since the
accident in 1986 (From Poïkarpov and Robeau, 2001)
Influx of
137
Cs
(TBq/a)
Average spectrum
activity of
137
Cs in the
Pripiat river (Bq/l)
Influx of
90
Sr
(TBq/a)
Average spectrum
activity of
90
Sr in the
Pripiat river (Bq/l)
1986 66,2 6,95 27,6 2,9
1987 12,8 1,65 10,4 1,34
1988 9,48 0,73 18,7 1,44
1989 6,44 0,521 8,97 0,725
1990 4,63 0,359 10,1 0.783
1991 2,9 0,208 14,4 1,033
1992 1,92 0,206 4,14 0,445
1993 3,48 0,208 14,2 0,838
1994 2,96 0,197 14,2 0,946
1995 1,15 0,11 3,4 0,326
1996 1,3 0,129 3,42 0,340
1997 1,7 0,158 2,68 0,25
1998 2,95 0,137 6,37 0,296
More than 16 years after the accident, only 2 to 3% of the deposited
radioactivity still remains in the aerial part of the vegetation.
Since the accident, wood marketing has become regulated. Depending
upon the intended use of harvested wood regulatory levels vary from 740 to
11 000 Bq
137
Cs kg
-1
, which result in 30% of the Pine trees in the exclusion zone
not being harvestable.
At this stage in time, the transfer of material by resuspension from more
to less contaminated areas is not significant. The classical farming practices,
mechanical treatment such as ploughing and mulching and the use of fertilisers
are efficient countermeasures.
However, one year after the accident a storm resuspended deposited
radioactivity in the exclusion zone, and the radioactivity of air in the Pripiat city
increased by a factor of 1 000 and reached 300 Bq.m
-3
. Fires in forests have also
led to increases of radioactivity. In 1992, in the vicinity of exclusion zone,
radioactivity due to forest fires reached 20 Bq.m
-3
for beta emitters and
70 mBq.m
-3
from plutonium isotopes. Monitoring stations far from these zones
registered some peaks of radioactivity.
51
In summary
It can be stated that there is now a fairly accurate estimate of the total
radioactivity release, and the last years have strengthened previous evaluations.
The duration of the release was unexpectedly long, lasting more than a week
with two periods of intense release. Another peculiar feature was the significant
emission (about 4%) of fuel material which also contained embedded
radionuclides of low volatility such as cerium, zirconium and the actinides. The
composition and characteristics of the radioactive material in the plume changed
during its passage due to wet and dry deposition, decay, chemical trans-
formations and alterations in particle size. The area affected was particularly
large due to the high altitude and long duration of the release as well as changes
in wind direction. However, the pattern of deposition was very irregular, and
significant deposition of radionuclides occurred where the passage of the plume
coincided with rainfall. Although all the Northern hemisphere was affected,
only territories of the former Soviet Union and part of Europe experienced
contamination to a significant degree. The environmental behaviour of
deposited radionuclides is increasingly well known. More than sixteen years
after the accident, radionuclides are still in the first layers of soils, maintaining a
transfer to plants, particularly mushrooms, berries and forest products.
Moreover the change of speciation of
137
Cs in some soils has led to the fact that
foodstuffs will remain contaminated for much longer than initially expected
(Sm00). With the exception of some water tables, the contamination of
environment is very well known. Contamination levels in soils decrease only
slowly, mostly by transfer to plants. Most of the decrease in the coming years
will be at only the rate of the physical half-life of
137
Cs.
53
Chapter III
REACTIONS OF NATIONAL AUTHORITIES
The scale and severity of the Chernobyl accident with its widespread
radioactive contamination had not been foreseen and took by surprise most
national authorities responsible for emergency preparedness. No provisions had
been made for an accident of such scale and, though some radiation protection
authorities had made criteria available for intervention in an accident, these
were often incomplete and provided little practical help in the circumstances, so
that very few workable national guidelines or principles were actually in place.
Those responsible for making national decisions were suddenly faced with an
accident for which there were no precedents upon which to base their decisions.
In addition, early in the course of the accident there was little information
available, and considerable political pressure, partially based on the public
perception of the radiation danger, was being exerted on the decision makers. In
these circumstances, cautious immediate action was felt necessary, and
measures were introduced that tended to err, sometimes excessively so, on the
side of prudence rather than being driven by informed scientific and expert
judgement.
Within the former Soviet Union
The town of Pripyat was not severely contaminated by the initial release
of radionuclides, but, once the graphite fire started, it soon became obvious that
contamination would make the town uninhabitable. Late on 26 April it was
decided to evacuate the town, and arrangements for transport and
accommodation of the evacuees were made. The announcement of evacuation
was made at 11:00 hr the following day. Evacuation began at 14:00 hr, and
Pripyat was evacuated in about two and one half hours. As measurements
disclosed the extensive pattern of deposition of radionuclides, and it was
possible to make dose assessments, the remainder of the people in a 30-km zone
around the reactor complex were gradually evacuated, bringing the total
evacuees to about 135 000.
54
Other countermeasures to reduce dose were widely adopted (Ko90).
Decontamination procedures performed by military personnel included the
washing of buildings, cleaning residential areas, removing contaminated soil,
cleaning roads and decontaminating water supplies. Special attention was paid
to schools, hospitals and other buildings used by large numbers of people.
Streets were watered in towns to suppress dust. However, the effectiveness of
these countermeasures outside the 30-km zone was small. An attempt to reduce
thyroid doses by the administration of stable iodine to block radioactive uptake
by the thyroid was made (Me92), but its success was doubtful.
The Soviet National Committee on Radiation Protection (NCRP)
proposed a 350-mSv lifetime dose intervention level for the relocation of
population groups (Il87). This value was lower by a factor of 2 to 3 than that
recommended by the International Commission on Radiological Protection
(ICRP) for the same countermeasure. Nevertheless, this value proposed by the
NCRP was strongly criticised as being a very high level. The situation was
further complicated by the political and social tension in the Soviet Union at
that time. As a result, the NCRP proposal was not adopted by the Supreme
Soviet. Later, a special Commission was established which developed new
recommendations for intervention levels. These recommendations were based
on the levels of ground contamination by the radionuclides
137
Cs,
90
Sr and
239
Pu.
As has been mentioned above, large areas were contaminated mainly by
137
Cs
and a ground contamination level by this radionuclide of 1 480 kBq/m
2
was
used as the intervention criterion for permanent resettlement of population, and
of 555 to 1 480 kBq/m
2
for temporary relocation.
People who continued to live in the heavily contaminated areas were
given compensation and offered annual medical examinations by the
government. Residents of less contaminated areas are provided with medical
monitoring. Current decisions on medical actions are based on annual doses.
Compensation is provided for residents whose annual dose is greater than
1mSv. The use of locally produced milk and mushrooms is restricted in some of
these areas. Relocation is considered in Russia for annual doses above 5 mSv.
As is mentioned in the section on health impacts effects, in Chapter V,
the Soviet authorities did not foresee that their attempts to compensate those
affected by the accident would be misinterpreted by the recipients and increase
their stress, and that the label of “radiophobia” attributed to these phenomena
was not only incorrect, but was one that alienated the public even more. Some
of these initial approaches have been recognised as being inappropriate and the
authorities are endeavouring to rectify their attitude to the exposed population.
55
Outside the former Soviet Union
The progressive spread of contamination at large distances from the
accident site has caused considerable concern in Member countries, and the
reactions of national authorities to this situation have been extremely varied,
ranging from a simple intensification of the normal environmental monitoring
programmes, without adoption of any specific countermeasures, to compulsory
restrictions concerning the marketing and consumption of foodstuffs. This
variety of responses has been accompanied by significant differences in the
timing and duration of the countermeasures.
In general, the most widespread countermeasures were those which were
not expected to impose, in the short time for which they were in effect, a
significant burden on lifestyles or the economy. These included advice to wash
fresh vegetables and fruit before consumption, advice not to use rainwater for
drinking or cooking, and programmes of monitoring citizens returning from
potentially contaminated areas. In reality, experience has shown that even these
types of measures had, in some cases, a negative impact which was not
insignificant.
Protective actions having a more significant impact on dietary habits and
imposing a relatively important economic and regulatory burden included
restrictions or prohibitions on the marketing and consumption of milk, dairy
products, fresh leafy vegetables and some types of meat, as well as the control
of the outdoor grazing of dairy cattle. In some areas, prohibitions were placed
on travel to areas affected by the accident and on the import of foodstuffs from
the Soviet Union and Eastern European countries. In most Member countries,
restrictions were imposed on the import of foodstuffs from Member as well as
non-member countries.
The range of these reactions can be explained primarily by the diversity
of local situations both in terms of uneven levels of contamination and in terms
of national differences in administrative, regulatory and public health systems.
However, one of the principal reasons for the variety of situations observed in
Member countries stems from the criteria adopted for the choice and application
of intervention levels for the implementation of protective actions. In this
respect, while the general radiation protection principles underlying the actions
taken in most Member countries following the accident have been very similar,
discrepancies arose in the assessment of the situation and the adoption and
application of operational protection criteria. These discrepancies were further
enhanced by the overwhelming role played in many cases by non-radiological
factors, such as socio-economic, political and psychological, in determining the
countermeasures.
56
This situation caused concern and confusion among the public,
perplexities among the experts and difficulties to national authorities, especially
in maintaining their public credibility. This was, therefore, identified as an area
where several lessons should be learned from the accident and efforts directed
towards better international harmonisation of the scientific bases and co-
ordination of concepts and measures for the protection of the public in case of
emergency.
Nowhere was this problem better illustrated than by the way that
contaminated food was handled. In some countries outside the Soviet Union the
main source of exposure to the general population was the consumption of
contaminated food. Mechanisms to handle locally produced as well as imported
contaminated food had to be put in place within a few weeks of the accident.
National authorities were in an unenviable position. They had to act quickly and
cautiously to introduce measures to protect the “purity” of the public food
supply and, what is more, they had to be seen to be effective in so doing. This
inevitably led to some decisions which even at the time appeared to be over-
reactions and not scientifically justified. In addition, dissenting opinions among
experts added to the difficulties of the decision makers.
Some countries without nuclear power programmes and whose own food
was not contaminated, argued that they did not need to import any “tainted”
food and refused any food containing any radionuclides whatsoever. This
extreme and impracticable measure might well have been regarded as an
example of how well the authorities of those countries were protecting the
health of their population. Sometimes this attitude appeared to promote a
neighbourly rivalry between countries to see which could set the more stringent
standards for food contamination, as though, by so doing, their own citizens
were more protected. The result was that often slightly contaminated food was
destroyed or refused importation to avoid only trivial doses.
In 1986, the EC imposed a ban on the importation of food containing
more than 370 Bq/kg of radiocaesium for milk products and 600 Bq/kg for any
other food, regardless of the quantity consumed in the average European diet.
Thus, food items with a trivial consumption (and dose), such as spices, were
treated the same as items of high consumption such as vegetables. However,
these values were later relaxed for some food items in order to remove
inconsistent treatment of food groups.
In some special circumstances, decisions had to be made based on the
local situation. For example, in some Northern European communities, reindeer
meat is a major component of the diet; due to the ecological circumstances,
these animals tend to concentrate radiocaesium, which will then expose the
57
populations which depend on them. Special countermeasures, such as pasturing
reindeer in areas of lower contamination, were introduced in some countries to
avoid this exposure.
The variety of solutions led to confusion and made any international
consensus on Derived Intervention Levels for food extremely difficult to
achieve, and it was only with the WHO/FAO Codex Alimentarius Meeting in
Geneva in 1989 that any agreement was reached on guideline values for the
radioactivity of food moving in international trade (Table 4).
Table 4. Codex Alimentarius Guideline values for food moving
in international trade (FA91)
Foods for general consumption
Radionuclide Level (Bq/kg)
241
Am,
239
Pu
90
Sr
131
I,
134
Cs,
137
Cs
10
100
1 000
Infant foods and milk
241
Am,
239
Pu
131
I,
90
Sr
134
Cs,
137
Cs
1
100
1 000
It should be remembered that these guideline values were developed to
facilitate international trade in food, and should be regarded as levels “below
which no restrictions to trade need be implemented for radiological reasons”.
Levels above these do not necessarily constitute a health hazard, and if found,
the competent national authority should review what action should be taken.
Often the national authorities were not able accurately to predict the
public response to some of their advice and pronouncements. For example, in
some European countries, soon after the accident the public were advised to
wash leafy vegetables. The national authority felt that this was innocuous advice
as most people washed their vegetables anyway, and they were unprepared for
the public response which was to stop buying these vegetables. This resulted in
significant economic loss to local producers which far outweighed any potential
benefit in terms of radiological health.
58
In some countries, the public was told that the risks were very small but,
at the same time, were given advice on how to reduce these low risks. It was
very difficult to explain this apparently contradictory advice, and the national
authority came under criticism from the media (Sj87). Outside the Soviet
Union, the initial confusion led to inconsistent and precipitate actions which,
although understandable, were sometimes ill-advised and unjustified.
However, it should be emphasised that great progress has been made
since this early confusion. As a result of the actions of the international
organisations to harmonise intervention criteria and the willingness of countries
to cooperate in this endeavour, a firm groundwork for uniform criteria based on
accepted radiation protection principles has been established, so that relative
consistency can hopefully be expected in their implementation in the event of a
possible future nuclear accident.
More recent decisions
Today, territories where populations receive a dose lower than 1 mSv per
year are declared as zones permitting normal life. For areas higher than
1 mSv/year authorities continue to give social compensations, depending on the
dose. Areas where annual dose is higher than 20 mSv per year are exclusion
zones. With the new estimation of doses, some settlements in Russia have lost
their status as contaminated area by a decree (N° 5924, 18 December 1997)
which came into operation the 1 February 1998. This decision was badly
received by local populations and local authorities.
The opposite is also true, as of the 1
st
of January 1999, 8 397 people were
still living in areas where evacuation is an obligation (contamination higher than
30 Ci.km
-2
).
The relocation of evacuees has not been completely resolved, as of 2000,
more than 11 000 evacuees are still living in temporary provisory settlements.
Limits on trade exchange of agricultural productions were the same for
the three republics up to 1997. They were lowered a first time in 1987, a second
time in 1991 in the three republics, but in Ukraine these limits were lowered a
fourth time on 25 June 1997 and now apply to four main products: 100 Bq per
litre for milk (instead of 370 Bq/l in 1991); 200 Bq/kg for meat (instead 740 in
1991); 20 Bq/kg for bread and potatoes (instead of, respectively, 370 and 600
since 1991). In Russia, with the exception of Briansk, and Kalouga areas (jizdra,
Khvastovitchi and Oulianovskii), a new regulation was adopted the first of
59
March 1998 (SanPiN 2.3.2.560-96) for agricultural products and for milk the
limit is now 50 Bq.kg
-1
of
137
Cs (Bo99) (Table 5).
Table 5. Evolution of limits for trade exchange since 1986 in Russia,
Bielorussia and Ukraine, the italics values for 1997 are only for Ukraine
06 May 86 30 may 86 87 88 91 93
97
(Ukraine)
98
(Russia)
Milk 3700 370 370 370 370 370 100 50
Meat 3 700 1 850 1 850 740 740 200
Bread 370 370 370 370 370 20
Potatoes 3 700 740 740 600 600 20
In Russia, more than ten years after the accident, several programmes
have been agreed upon to compensate for the delays in the implemantation of
previous plans. A national centre of ecological medicine has been created in
St.-Petersburg for health assistance to the liquidators. It can provide up to
1 500 sick people per year with high quality medical treatment. This centres was
expanded to other national hospitals in the Russian federation. Ten expert
councils have been created to establish a potential links between diseases and
the Chernobyl accident. Four socio-psychological readaptation centres have
been created in the Bryansk, Orel and Toula areas in Russia. These centers have
been charged with delivering justice, social and psychological assistance to all
those affected by the accident. Lastly a dosimetry register has been created, in
1999, in which more than 500 000 people have been registered (including
170 000 liquidators).
Several significant programmes were launched during 1998-2000, to take
in account the huge delay of all national programmes, Including a National
programme for the protection of the public, a Programme for Chernobyl
children, and a Programme for settlements for liquidators (Bo99).
Lastly the Russian authorities are aware that some aspects of current
federal law must be changed to eliminate significant obstacles to ending certain
programmes that no longer contribute to the elimination of the consequences of
the accident.
60
In summary
The Chernobyl accident took authorities by surprise as regards to its
extent, duration and far reaching contamination. As there were no guidelines for
such an accident, little information was available and great political and public
pressure to do something were experienced, overprecautious decisions were
often taken in and outside the Soviet Union. The social and psychological
impact of some official decisions on the public were not expacted, and variable
interpretations or even misinterpretations of ICRP recommendations, especially
for intervention levels for food, led to inconsistent decisions and advice. These
added to public confusion and provoked mistrust and unnecessary economic
losses. However, there were exceptions, and very soon international efforts
began to harmonise criteria and approaches to emergency management.
More than 16 years later the confusion still exist in spite of significant
international efforts of harmonization. For example, in 1997 the Ukrain
unilaterally lowered its radiological restrictions on trade, below the levels
previously harmonised for Russia, Belarus and the Ukraine, reinforces this
confusion. Lastly, the Russian federation has realised the need to change some
apects of its former law, which has become an obstacle to appropriately
addressing accident consequences.
61
Chapter IV
DOSE ESTIMATES*
The exposure of the population as a result of the accident resulted in two
main pathways of exposure. The first is the radiation dose to the thyroid as a
result of the concentration of radioiodine and similar radionuclides in the gland.
The second is the whole-body dose caused largely by external irradiation
mainly from radiocesium.
The absorbed dose to the whole body is thought to be about 20 times
more deleterious, in terms of late health effects incidence, than the same dose to
the thyroid (IC90).
The population exposed to radiation following the Chernobyl accident
can be divided into four categories: (1) the staff of the nuclear power plant and
workers who participated in clean-up operations (referred to as “liquidators”);
(2) the nearby residents who were evacuated from the 30-km zone during the
first two weeks after the accident; (3) the population of the former Soviet
Union, including especially the residents of contaminated areas; and (4) the
population in countries outside the former Soviet Union.
A number of liquidators, estimated at up to 600 000 (civilian and military
according to laws promulgated in Belarus, the Russian Federation and Ukraine)
took part in mitigation activities at the reactor and within the 30-km zone
surrounding the reactor. The most exposed workers were the firemen and the
power plant personnel during the first days of the accident. Most of the dose
received by the workers resulted from external irradiation from the fuel
fragments and radioactive particles deposited on various surfaces. Of particular
interest are the 226 000 recovery operation workers who were employed in the
30-km zone in 1986-1987, as it is in this period that the highest doses were

* Special thanks to Dr. André Bouville, of the US National Cancer Institute, for his
verification of the facts in this Chapter.
62
received. The remainder of the recovery operation workers, who generally
received lower doses, amounted to about 400 000 (UN00).
About 116 000 people were evacuated during the first days following the
accident, mainly from the 30-km zone surrounding the reactor. Prior to
evacuation, those individuals were exposed to external irradiation from
radioactive materials transported by the cloud and deposited on the ground, as
well as to internal irradiation essentially due to the inhalation of radioactive
materials in the cloud.
The relative contributions to the external whole-body dose from the main
radionuclides of concern for that pathway of exposure and during the first few
months after the accident are shown in Figure 8. It is clear that
132
Te played a
major role in the first week after the accident, and that, after one month, the
radiocaesiums (
134
Cs and
137
Cs) became predominant. Subsequently, however,
134
Cs decayed to levels much lower than those of
137
Cs, which became after a
few years the only radionuclide of importance for practical purposes. It is usual
to refer to
137
Cs only, even when the mix of
134
Cs and
137
Cs is meant, because
the values for the constituents can be easily derived from those for
137
Cs.
With regard to internal doses from inhalation and ingestion of
radionuclides, the situation is similar: radioiodine (
131
I) was important during
the first few weeks after the accident and gave rise to thyroid doses via
inhalation of contaminated air, and, more importantly, via consumption of
contaminated foodstuffs, mainly cow’s milk. After about one month, the
radiocaesiums (
134
Cs and
137
Cs) again became predominant, and, after a few
years,
137
Cs became the only radionuclide of importance for practical purposes,
even though
90
Sr may in the future play a significant role at short distances from
the reactor.
Among the population of the former Soviet Union, it is usual to single out
the residents of the contaminated areas, defined as those with
137
Cs deposition
levels greater than 37 kBq/m
2
. About 5 million people live in such areas. Of
special interest are the inhabitants of the spots with
137
Cs deposition levels
greater than 555 kBq/m
2
. In those areas, called “strict control zones”, protection
measures are applied, especially as far as control of consumption of
contaminated food is concerned. In 1998, 42 554 measurements were performed
in the Federal Republic of Russia, and the national authorities are planning to
maintain such controls beyond 2000 (Bo99). In 1986, shortly after the accident,
the All-Union Dose Registry (AUDR) was set up by the Soviet Government to
record medical and dosimetric data on the population groups expected to be the
most exposed: (1) the liquidators, (2) the evacuees from the 30-km zone, (3) the
inhabitants of the contaminated areas, and (4) the children of those people. In
63
1991, the AUDR contained data on 659 292 persons. Starting from 1992,
national registries in Belarus, Russian Federation, and Ukraine replaced the
AUDR.
Outside the former Soviet Union, the radionuclides of importance are,
again, the radioiodines and radiocaesiums, which, once deposited on the ground,
give rise to doses from ingestion through the consumption of foodstuffs.
Deposited radiocaesium is also a source of long-term exposure from external
irradiation from the contaminated ground and other surfaces. Most of the
population of the Northern hemisphere was exposed, in varying degrees, to
radiation from the Chernobyl accident. The
137
Cs deposition outside the former
Soviet Union ranged from negligible levels to about 50 kBq/m
2
.
The liquidators
Most of the liquidators can be divided into two groups: (1) the people
who were working at the Chernobyl power station at the time of the accident
viz. the staff of the station and the firemen and people who went to the aid of
the victims. They number a few hundred persons; and (2) the workers, estimated
to amount up to 600 000, who were active in 1986-1990 at the power station or
in the zone surrounding it for the decontamination, sarcophagus construction
and other recovery operations.
On the night of 26 April 1986, about 400 workers were on the site of the
Chernobyl power plant. As a consequence of the accident, they were subjected
to the combined effect of radiation from several sources: (1) external
gamma/beta radiation from the radioactive cloud, the fragments of the damaged
reactor core scattered over the site and the radioactive particles deposited on the
skin, and (2) inhalation of radioactive particles (UN88).
All of the dosimeters worn by the workers were over-exposed and did not
allow an estimate of the doses received. However, information is available on
the doses received by the 237 persons who were placed in hospitals and
diagnosed as suffering from acute radiation syndrome. Using biological
dosimetry, it was estimated that 41 of these patients received whole-body doses
from external irradiation in the range 1-2 Sv, that 50 received doses between
2 and 4 Sv, that 22 received between 4 and 6 Sv, and that the remaining
21 received doses between 6 and 16 Sv. In addition, it was estimated from
thyroid measurements that the thyroid dose from inhalation would range up to
about 20 Gy, with 173 individuals in the 0-1.2 Gy range and seven workers with
thyroid doses greater than 11 Gy (UN88). Internal exposure of those workers
was mainly due to
131
I and shorter-lived radioiodines, the median value of the
64
ratio of the internal thyroid dose to the external effective dose was estimated to
be 0.3 Gy per Sv. The doses resulting from intakes of other radionuclides was
estimated to about 30 mSv for the early months following the accident and
85 mSv for committed dose (UN00).
The second category of liquidators consists of the large number of adults
who were recruited to assist in the clean-up operations. They worked at the site,
in towns, forests and agricultural areas to make them fit to work and live in.
About 600 000 of individuals participated in this work. Initially, about 240 000
of those workers came from the Soviet armed forces, the other half including
personnel of civil organisations, the security service, the Ministry of Internal
Affairs, and other organisations. The total number of liquidators has yet to be
determined accurately, since only some of the data from some of those
organisations have been collected so far in the national registries of Belarus,
Russia, Ukraine and other republics of the former Soviet Union (So95). Also, it
has been suggested that, because of the social and economic advantages
associated with being designated a liquidator, many persons have contrived
latterly to have their names added to the list. To day the total number of
recovery operation workers recorded in the registries appears to be about
400 000 well below the figure of 600 000, which corresponds to the number of
people who have received special certificates confirming their status as
liquidators. The workers were all adults, mostly males aged 20-45 years.
There are only fragmented data on the doses received by these
liquidators. Attempts to establish a dosimetric service were inadequate until the
middle of June of 1986, until then, doses were estimated from area radiation
measurements. The doses to the recovery operation workers who participated in
mitigation activities within two months after the accident are not known with
much certainty. The liquidators were initially subjected to a radiation dose limit
for one year of 250 mSv. In 1987 this limit was reduced to 100 mSv and in
1988 to 50 mSv (Ba93). The registry data show that the average recorded doses
in the three national registries decreased from year to year, being about
170 mSv in 1986, 130 mSv in 1987, 30 mSv in 1988 and 15 mSv in 1989
(Se95a). It is, however, difficult to assess the validity of the results as they have
been reported since these statistics indicates that the dose is known for only
52% of workers for the period 1986-1989, with a lower percentage, 45% for the
first year. Moreover uncertainties associated with dose estimations are assessed
to be up to 50% for individual dosimetry, (if the dosimeter was correctly used),
up to a factor 3 to 5 for group and time-and-motion dosimetry However, the
doses do not seem to have been systematically overestimated, because
biological dosimetry performed on limited number of workers produced results
compatible with physical dose estimates.
65
It is interesting to note that a small special group of 672 scientists from
the Kurchatov Institute who have worked periodically inside the sarcophagus
for a number of years have initially estimated accumulated whole-body doses in
the range 0.5 to 13 Gy (Se95a). These dose estimates had been reestimated.
Recorded and calculated doses available for 501 workers show that more than
20% of them received doses between 0.05 and 0.25 Sv and about 5% of them
received doses between 0.25 and 1.5 Sv (Sh97) Additional analysis by mean of
FISH technique for three of them resulted in doses 0.9, 2.0 and 2.7 Sv (Sh00)
While no deterministic effects have been noted to date, this group may well
show radiation health effects in the future.
More than sixteen years after the accident, comparisons between the
different techniques of dosimetry confirm the effectiveness of the chromosome
aberration technique, but indicate that some new methods recommended by
some scientists, such as fluorescent in situ hybridisation (FISH), do not appear
to be a sufficiently sensitive or specific to allow the estimation of doses for the
majority of recovery operation workers (Li98).
The evacuees from the 30-km zone
Immediately after the accident monitoring of the environment was started
by gamma dose rate measurements. About 20 hours after the accident the wind
turned in the direction of Pripyat, gamma dose rates increased significantly in
the town, and it was decided to evacuate the inhabitants. About 20 hours later
the 49 000 inhabitants of Pripyat had left the town in nearly 1 200 buses. About
a further 67 000 people were evacuated in the following days and weeks (in
fact, until September) from the contaminated areas (a number of 86 000 people
given in the NEA’s 1996 report (NE95b) was not substantiated).
Information relevant for the assessment of the doses received by these
people have been obtained by 30 000 responses of the evacuees to
questionnaires about the location where they stayed, the types of houses in
which they lived, the consumption of stable iodine, and other activities (Li94).
The average effective dose from external irradiation was estimated to be
17 mSv, with individual values varying from 0.1 to 380 mSv (Li94). This value
is concordant with the absorbed dose of 20 mGy estimated by Electron Spin
resonance (ESR) measurements of sugar and exposure rate calculations (Na94).
The main source of uncertainty in the estimation of the average effective
doses from external irradiation is the assessment of the activity ratios of
132
Te
and
131
I to
137
Cs in the deposition.
66
Doses to the thyroid gland
The iodine activity in thyroid glands of evacuees was measured. More
than about 5 000 measurements of former inhabitants of Pripyat had sufficient
quality to be useful for dose reconstruction (Go95a). A comparative analysis
with the questionnaire responses of 10 000 evacuees showed that thyroid doses
were mainly due to inhalation of
131
I. Average individual doses and collective
doses to the thyroid are shown in Table 6 for three age groups. Individual doses
in the age classes were distributed over two orders of magnitude. The main
factor influencing the individual doses was found to be the distance of the
residence from the reactor.
Table 6. Average doses to the thyroid gland and collective thyroid doses to
the evacuees from Pripyat (Go95a)
Year of birth Number of
people
Average individual
dose (Gy)
Collective dose
(person-Gy)
1983-1986
1971-1982
≤1970
2 400
8 100
38 900
1.4
0.3
0.07
3 300
2 400
2 600
Assessments of the doses to the thyroid gland of the evacuees from the
30-km zone (Li93a) showed similar doses for young children as those for the
Pripyat evacuees. Exposures to adults were higher. These high doses were due
to a greater consumption of food contaminated with
131
I among those evacuated
later from the 30-km zone.
Whole-body doses
The whole-body doses to the evacuees were mainly due to external
exposure from deposited
132
Te/
132
I,
134
Cs and
137
Cs and short lived radionuclides
in the air. Measurements of the gamma dose rate in air were performed every
hour at about thirty sites in Pripyat and daily at about eighty sites in the 30-km
zone. Based on these measurements and using the responses to the
questionnaires, whole-body doses were reconstructed for the 90 000 persons
evacuated from the Ukrainian part of the 30-km zone (Li94). There was a wide
range of estimated doses with an average value of 15 mSv. The collective dose
was assessed to be 1 300 person-Sv. The 24 000 persons evacuated in Belarus
might have received slightly higher doses, since the prevailing wind was
initially towards the north.
67
The estimates of collective doses for the populations that were evacuated
in 1986 from the contaminated areas of Belarus, Russia and Ukraine was about
3 800 man Sv for effective dose and 25 000 man Gy for thyroid doses (UN00).
Most of the collective doses were received by the populations of Belarus and
Ukraine.
Because the distributions of iodine tablets was done with a one-week
delay and because only part of the population was covered, the averted
collective thyroid dose from ingestion of contaminated milk was about 30% of
the expected collective thyroid dose from that pathway while the thyroid doses
from inhalation remained unchanged.
People living in the contaminated areas
Areas contaminated by the Chernobyl accident have been defined with
reference to the background level of
137
Cs deposition caused by the atmospheric
weapons tests, which when corrected for radioactive decay to 1986, is about
2-4 kBq m
-2
. considering variations about this level, it is usual to specify the
level of 37 kBq m
-2
as the area affected by the Chernobyl accident.
Approximately 3% of the European part of the former USSR was
contaminated with
137
Cs deposition density greater than 37 kBq.m
-2
. Many
people continue to live in these contaminated territories, although efforts have
been made to limit their doses, 4 400 000 inhabitants were living in areas with a
137
Cs contamination ranging from 37 to 185 kBq.m
-2
, 580 000 in areas
185-555 kBq.m
-2
. Areas of
137
Cs deposition density greater than 555 kBq km
-2
were designated as areas of strict control. In these areas, preventive measures
have been successfully maintained annual effective dose below 5 mSv. Because
of extensive migration, the number of people living in these areas under strict
control was about 193 000 people in 1995, down from 273 000 in 1986-1987.
In the first few months, because of the significant release of the short-
term
131
I, the thyroid was the most exposed organ, the main route of exposure
was cow-milk pathway. During the first year after the accident, doses from
external irradiation arose from ground deposition of radionuclides with half-
lives of one year or less only in areas close to the reactor, but the radiocesiums
deposition was the greater contributors in more distant areas only one month
after the accident. Over the following years, the doses received by the
populations living in contaminated areas have come essentially from external
exposure due to
134
Cs and
137
Cs deposited on the soil and internal exposure due
to contamination of foodstuffs by these two isotopes.
68
A very large number of measurements have been done in the three
republics. The publications prepared for regulatory purposes, tend to over
estimate the average doses that were received during the years 1986-1990.
Figure 8. Contributions of radionuclides to the absorbed dose rate in air in
a contaminated area of the Russian Federation during the first
several months after the Chernobyl accident
80
70
60
50
40
30
20
10
0
0 10 20 30 40 50 60 70 80 90 100 110 120 130 140 150
132 132
Te + I
140 140
Ba + La
134
Cs
106
Ru
131
I
Other
137
Cs
Time after accident (days)
P
e
r
c
e
n
t
a
g
e
Credit: Sources and Effects of Ionising Radiation – United Nations Scientific Committee on
the Effects of Atomic Radiation – UNSCEAR 2000 report to the General Assembly with
Scientific Annexes – Volume II: Effects, United Nations.
69
Doses to the thyroid gland
The main information source for the dose reconstruction is the vast
number of iodine activity measurements of thyroid glands. In Ukraine
150 000 measurements, in Belarus several hundreds of thousands of measure-
ments and in the Russian Federation more than 60 000 measurements were
performed in May/June 1986. Some of the measurements were performed with
inadequate instrumentation and measurement conditions and are not useful for
dose assessment purposes. Using these measurements, the thyroid dose for
people who lived in areas where direct thyroid measurements were done within
a few weeks after the accident are being reconstructed using available data on
131
I and
137
Cs deposition.
The influence of having taken stable iodine for prophylactic purposes has
usually not been taken into account in the determination of thyroid doses
(except for the evacuees from Pripyat, iodine prophylaxis was not effective in
reducing the doses substantially as it was done too late).
The large variability of individual doses makes estimates of dose
distributions difficult and current dose estimates are still subject to considerable
uncertainties, especially in areas where only a few activity measurements in the
thyroid were performed. Children in the Gomel oblast (region) in Belarus
received the highest doses. The distribution of estimated individual doses in the
thyroid of 0-7 years children is shown in Table 7.
Table 7. Distribution of estimated individual doses in the thyroid of
0-7 years old children in Gomel and Mogilev contaminated districts
Gomel Mogilev Total
<0.05 784 256 1040
0.05-0.1 527 339 866
0.1-0.3 1762 586 2348
0.3-1 3573 476 4049
1-2 1983 119 2102
>2 5727 44 5771
70
For the total population of Belarus, the average dose to the thyroid is
0.9 to 1 Gy for 0-7-year-old children and 0.3 Gy for the total population giving
collective doses of 34 000 and 134 000 man Gy respectively. (Il91) For the
populations of the three republics, the collective thyroid doses are roughly
estimated to 550 000, 200-300 000, 390 000 man Gy for Belarus, Russian
Federation and Ukraine respectively (UN00). The average thyroid dose received
by the populations of the three republics is estimated to be 7 mGy and
exceeding 1 Gy for the most exposed children (UN00). In the eight most
contaminated districts of Ukraine where thyroid measurements were performed,
the collective dose to this age group was about 60 000 person-Sv and for the
whole population about 200 000 person-Sv (Li93). In the Russian Federation
the collective dose to the whole population was about 100 000 person-Sv
(Zv93).
The thyroid doses are about two times greater in rural areas than in urban
aeras.
An estimate of the dose distribution among children from Gomel oblast is
shown in Table 8. For the whole Belarus the collective thyroid dose to children
(0 to 14 years) at the time of the accident was assessed to be about
170 000 person-Gy (Ri94). To day the UNSCEAR report give an estimation of
34 000 man Gy to 0-7 year old children (UN00).
Table 8. Distribution of thyroid doses to children (0-15 years)
in the Gomel oblast of Belarus (from UN00)
<1 year 1-7 years 8-15 years
<0.05 134 650 1 058
0.05-0.1 58 469 884
0.1-0.3 224 1 538 2 998
0.3-1 587 2 986 4 729
1-2 318 1 665 1 563
>2 3 667 2 060 1 107
In some Russian villages average doses exceeded 1 Gy, and individual
doses exceeded 10 Gy.
Limited information is available on in utero thyroid doses. In a study in
250 children, born between may 1986 and February 1987 in Belarus, thyroid
71
doses were estimated to range up to 4.3 Gy, with 135 children exposed to less
than 0.3 Gy, 95 children between 0.3 and 1 Gy, and 20 children with doses
greater than 1.Gy (Ig99).
Evaluations of questionnaires on food consumption rates in the period
May/June 1986 and measurements of food contamination showed
131
I in milk as
the major source for the thyroid exposure of the population living in the
contaminated areas. However, in individual cases the consumption of fresh
vegetables contributed significantly to the exposure.
Whole-body doses
Two major pathways contributed to the whole-body doses of the
population in contaminated areas, the exposure to external irradiation from
deposited radionuclides (Iv95) and the incorporation into the body of radio-
caesium in food.
The external exposure is directly related to the radionuclide activity per
unit area and it is influenced by the gamma dose rates in air at the locations of
occupancy. Forestry workers and other workers living in woodframe houses
received the highest doses.
Most of the higher contaminated areas are rural and a large part of the
diet is locally produced. Therefore, the uptake of caesium by the plants from the
soil is a deciding factor in the internal exposure. These are regions with
extraordinarily high transfer factors, as the Rovno region in Ukraine, where
even moderate soil contamination led to high doses. In order of decreasing
magnitude of transfer factors these regions are followed by regions with peaty
soil, sandy podzol (acidic infertile forest soil), loamy podzol, and chernozem
which is rich black soil.
In the first years after the accident the caesium uptake was dominated
practically everywhere by the consumption of locally produced milk (Ho94).
However, later mushrooms began to contribute significantly in many
settlements to the caesium incorporation for two reasons. First, the milk
contamination decreased with time, whereas the mushroom contamination
remained relatively constant. Second, due to changes in the economic
conditions in the three republics, people are collecting more mushrooms than
they were in the first years after the accident.
The normalised lifetime doses for urban and rural populations of the three
republics is now estimated to range from 42 to 88 6YSHUN%TP
-2
of
137
Cs, 60%
being received during the first 10 years. These values are lower than the first
72
estimates, because they are more realistic and take account of, for example, the
vertical migration of cesium in soils. During the first 10 years after the accident,
average effective doses in theses areas ranged from 5mSv in Russian urban
areas to 11 mSv in the rural areas of Ukraine. The variability of dose
distribution could be represented by a log-normal distribution with a geometric
standard deviation of 1.54. The decontamination measures had a limited impact
on members of population. It was expected that less than 15% of the dose could
be averted for the general population, and only 35% for school children. The
total averted collective dose attributable to decontamination procedures was
estimated to 1 500 mSv for the first four years.
The distribution of the collective dose from external irradiation by region
and dose interval are presented in Table 9 and 10.
Table 9. Estimated collective effective dose to the populations of
contaminated areas (1986-1995) excluding thyroid dose
Collective effective dose (man Gy) Region Population
External Internal Total
Belarus 1 880 612 9 636 5 504 15 140
Russian
Federation
1 983 000 8 450 4 990 13 440
Ukraine 1 296 000 6 100 7 860 13 960
Total 5 159 600 24 186 18 354 42 540
Table 10. Distribution of estimated total effective doses received by the
populations of contaminated areas (1986-1995) excluding thyroid dose
Number of persons
Dose interval (mGy) Belarus Russian
Federation
Ukraine
<1 133 053 155 301 –
1-5 1163 490 1 253 130 330 900
5-20 439 620 474 176 807 900
20-50 113 789 82 876 148 700
50-100 25 065 14 580 7 700
100-200 5 105 2 979 400
>200 790 333 –
73
Table 11 summarises an estimate of whole-body doses to people living in
the higher contaminated areas. On average, external irradiation was by far the
highest contributor to the total population exposure (Er94). However, the
highest doses to individuals were produced by the consumption of food from
areas with high transfers of radionuclides.
Table 11. Distribution of external and total whole-body doses
during 1986-89, to inhabitants of contaminated areas
(
137
Cs activity per unit area >555 kBq/m
2
) (Ba94)
Whole-body
dose (mSv)
External exposure Total exposure
No. of
persons
Collective dose
(man.Sv)
No. of
persons
Collective dose
(man.Sv)
5-20
20-50
50-100
100-150
150-200
>200
132 000
111 000
24 000
2 800
530
120
1 700
3 500
1 600
330
88
26
88 000
132 000
44 000
6 900
1 500
670
1 200
4 200
3 000
820
250
160
Total 270 000 7 300 273 000 9 700
The total collective effective dose received during the first 10 years after
the accident by the approximately 5.2 million people living in the contaminated
areas of Belarus, the Russian federation and Ukraine is estimated to be
24 200 man.Sv. This means, as ten years represents 60%, that the lifetime
collective dose from external irradiation would be 40 300 man.Sv (UN00).
Internal doses were 5 500 man Sv for Belarus, 5 000 man.Sv for the
Russian Federation an 7 900 man.Sv for Ukraine. As 10 years represents 90%,
the lifetime total for the three republics would be 20 400 man.Sv, corresponding
to an average individual lifetime effective dose of 3.9 mSv [UN00].
Total collective thyroid doses in Belarus, the Russian Federation,
and the Ukrain, respectivly, were estimated to be 550 000 250 000 and
740 000 man Gy.
The total of about 60 700 man Sv for external and internal doses
corresponds to an average individual lifetime effective dose of 12 mSv,
74
excluding thyroid collective dose delivered during the first year. This is
estimated to be 1 500 000 man Gy in total for the three countries.
Populations outside the former Soviet Union
Even though the releases of radioactive materials during the Chernobyl
accident mainly affected the populations of Belarus, Russia and Ukraine, the
released materials became further dispersed throughout the atmosphere and the
volatile radionuclides of primary importance (
131
I and
137
Cs) were detected in
most countries of the Northern hemisphere. However, population doses were, in
most places, much lower than in the contaminated areas of the former Soviet
Union; they reflected the deposition levels of
137
Cs and were higher in areas
where the passage of the radioactive cloud coincided with rainfall. Generally
speaking, however, and with a few notable exceptions, the doses decreased as a
function of distance from the reactor (Ne87).
During the first few weeks after the accident,
131
I was the main
contributor to the dose, via ingestion of milk (Ma91). Infant thyroid doses
generally ranged from 1 to 20 mGy in Europe, from 0.1 to 5 mGy in Asia, and
were about 0.1 mGy in North America. Adult thyroid doses were lower by a
factor of about 5 (UN88).
Later on,
134
Cs and
137
Cs were responsible for most of the dose, through
external and internal irradiation (Ma89). The whole-body doses received during
the first year following the accident generally ranged from 0.05 to 0.5 mGy in
Europe, from 0.005 to 0.1 mGy in Asia, and of the order of 0.001 mGy in North
America. The total whole-body doses expected to be accumulated during the
lifetimes of the individuals are estimated to be a factor of 3 greater than the
doses received during the first year (UN88).
In summary
A large number of people received substantial doses as a result of the
Chernobyl accident:
• Liquidators – Hundreds of thousands of workers, estimated to
amount up to 600 000, were involved in clean-up operations. The
most exposed, with doses of several grays, were the workers
involved immediately after the beginning of the accident and the
scientists who have performed special tasks in the sarcophagus. The
75
average doses to liquidators are reported to have ranged between
170 mSv in 1986 and 15 mSv in 1989.
• Evacuees – More than 100 000 persons were evacuated during the
first few weeks following the accident. The evacuees were exposed
to internal irradiation arising from inhalation of radioiodines,
especially
131
I, and to external irradiation from radioactivity present
in the cloud and deposited on the ground. Thyroid doses are
estimated to have been, on average, about 1 Gy for small children
under 3 years of age at the time of the accident, and about 70 mGy
for adults. Whole-body doses received from external irradiation prior
to evacuation from the Ukrainian part of the 30-km zone showed a
large range of variation with an average value of 15 mGy.
• People living in contaminated areas of the former Soviet Union –
About 270 000 people live in contaminated areas with
137
Cs
deposition levels in excess of 555 kBq/m2. Thyroid doses, due
mainly to the consumption of cow’s milk contaminated with
131
I,
were delivered during the first few weeks after the accident; children
in the Gomel region of Belarus appear to have received the highest
thyroid doses with a range from negligible levels up to 40 Gy and an
average close to 1 Gy for children aged 0 to 7. Thanks to the control
of foodstuffs in those areas, most of the radiation exposure has been
due to external irradiation from the
137
Cs activity deposited on the
ground; the whole-body doses for the 1986-1989 time period are
estimated to range from 5 to 250 mGy with an average of 40 mGy.
In areas without food control, there are places, such as the Rovno
region of Ukraine, where the transfer of
137
Cs from soil to plant is
very high, resulting in doses from internal exposure being greater
than those from external exposure.
• Populations outside the former Soviet Union – The radioactive
materials of a volatile nature (such as iodine and caesium) that were
released during the accident spread throughout the entire northern
hemisphere. The doses received by populations outside the former
Soviet Union were relatively low, and showed large differences from
one country to another depending mainly upon whether rainfall
occurred during the passage of the radioactive cloud.
77
Chapter V
HEALTH IMPACT
As ionising radiation passes through the body, it interacts with the tissues
transferring energy to cells and other constituents by ionisation of their atoms.
This phenomenon has been extensively studied in the critical genetic material,
DNA, which controls the functions of the cells. If the damage to DNA is slight
and the rate of damage production is not rapid, i.e. at low dose rate, the cell may
be able to repair most of the damage. If the damage is irreparable and severe
enough to interfere with cellular function, the cell may die either immediately or
after several divisions.
At low doses, cell death can be accommodated by the normal
mechanisms that regulate cellular regeneration. However, at high doses and
dose rates, repair and regeneration may be inadequate, so that a large number of
cells may be destroyed leading to impaired organ function. This rapid, cell death
at high doses leads to early deleterious radiation effects which become evident
within days or weeks of exposure, and are known as “deterministic effects”.
These deterministic effects can be life-threatening in the short term if the dose is
high enough, and were responsible for most of the early deaths in the Chernobyl
accident.
Lower doses and dose rates do not produce these acute early effects,
because the available cellular repair mechanisms are able to compensate for the
damage. However, this repair may be incomplete or defective, in which case the
cell may be altered so that it may develop into a cancerous cell, perhaps many
years into the future, or its transformation may lead to inheritable defects in the
long term. These late effects, cancer induction and hereditary defects, are
known as “stochastic effects” and are those effects whose frequency, not
severity, is dose dependent. Moreover, they are not radiation-specific and,
therefore, cannot be directly attributed to a given radiation exposure.
For this reason, low dose health effects in humans cannot be measured
and, therefore, risk projections of the future health impact of low-dose ionising
radiation exposure have to be extrapolated from measured high-dose effects.
78
The assumption is made that no dose of ionising radiation is without potential
harm, and that the frequency of stochastic effects at low doses is proportional to
that occurring at high doses. This prudent assumption has been adopted to assist
in the planning of radiation protection provisions when considering the
introduction of practices involving ionising radiations. The ICRP has estimated
the risk of fatal cancer to the general population from whole-body exposure to
be 5% per sievert (IC90).
The health impact of the Chernobyl accident can be classified in terms of
acute health effects (“deterministic effects”) and of late health effects
(“stochastic effects”). Moreover, there are also social and psychological effects
which can influence health.
Radiation induced health effects
Acute health effects
All the acute deterministic health effects occurred among the personnel of
the plant, or in those persons brought in for fire fighting and immediate clean-
up operations.
Two deaths were immediately associated with the accident: one person
killed by the explosion and another who suffered a coronary thrombosis. A third
person died early the morning of the accident from thermal burns. Twenty-eight
other persons died later in the treatment centres, bringing the total to 31 deaths
in the first weeks after the accident (UN88).
All symptomatic exposed persons from the site were placed in hospitals.
Of the total of 499 people were admitted for observation, 237 of these were
initially diagnosed as suffering from acute radiation syndrome. The severity and
rapidity of onset of their symptoms depended on their dose. The initial early
signs and symptoms of radiation sickness from high doses included diarrhoea,
vomiting, fever and erythema. Over 200 patients were placed in regional
hospitals and specialised centres in the first 24 hours. Patients were allocated to
four categories of radiation sickness severity according to their symptoms, signs
and dose estimates. The differential white blood cell count showed reduced
circulating lymphocytes (lymphocytopenia) which was the initial indicator of
the severity of the exposure and became evident in the first 24-36 hours for
those most severely irradiated.
79
No members of the general public received such high whole-body doses
as to induce Acute Radiation Syndrome (IA86). This was confirmed in Belarus,
where, between May and June 1986, 11 600 people were investigated without
the discovery of any cases of acute radiation sickness.
In the highest exposure group of those who were acutely exposed
(6-16 Gy), the first reaction was usually vomiting, occurring within
15-30 minutes of exposure. These patients were desperately ill; fever and
intoxication as well as diarrhoea and vomiting, were prominent features.
Mucous membranes were severely affected, becoming swollen, dry and
ulcerated, making breathing and swallowing extremely painful and difficult.
Extensive burns both thermal and due to beta radiation often complicated the
illness. Within the first two weeks white blood cells and platelets fell
dramatically, indicating a very high dose which had compromised the
production of blood cells in the bone marrow, making it virtually impossible for
the patients to fight infection or to retain the natural clotting activity of the
blood. Almost all the patients with such high doses died (20 of 21), in spite of
the intensive specialised medical treatment provided.
At lower exposures, the symptoms, signs and laboratory findings
improved. Vomiting began later, platelet and white cell counts did not drop so
precipitously and the fever and toxaemia were less pronounced. Beta radiation
burns to the skin were a major complicating factor and mucous membrane
damage was difficult to treat, but survival improved markedly at lower doses, so
that no early deaths were noted in the less than 1-2 Gy exposure group
(Table 12).
Table 12. Outcome of radiation exposure among persons hospitalised for
acute radiation syndrome
Number of patients Estimated dose (Gy) Deaths
21
21
55
140
6-16
4-6
2-4
less than 2
20
7
1
0
Total 237
28
There is a large range of medical treatments that can be attempted to
mitigate acute radiation syndrome. All these procedures were applied to the
persons hospitalised with varying degrees of success. The hospital treatment
following the accident included replacement therapy with blood constituents,
80
fluids and electrolytes, antibiotics, antifungal agents, barrier nursing and bone
marrow transplantation.
The treatment of the depression of bone-marrow function encountered
after the accident was largely supportive. Special hygienic measures were taken;
patients’ clothes were changed at least twice a day and aseptic techniques used.
Those patients who received doses above 2 Gy were given anti-fungal agents
after the second week. Antibiotics and gamma globulin were also administered.
Bone-marrow transplantation was undertaken in 13 patients who were
judged to have irreversible bone marrow damage after doses greater than 4 Gy.
All but two of these patients died, some before the transfused marrow had had a
chance to “take”, but others had short-term takes. It was concluded that, even
after very high radiation doses, the bone marrow may well not be completely
destroyed and may recover at least some function at a later stage. It is this
recovery which may lead to later rejection of the transplanted marrow through a
“Host versus Graft” reaction. The physicians responsible for treating the victims
of the accident concluded that bone marrow transplantation should play a very
limited role in treatment.
Burns, both thermal and from beta radiation, were treated with surgical
excision of tissue that was not viable, and any fluid and electrolyte loss was
compensated for by the parenteral feeding set up to treat the gastro-intestinal
syndrome which is a prominent feature of acute radiation sickness. The oro-
pharyngeal syndrome of mucosal destruction, oedema and the absence of
lubrication caused by radiation damage to the mucosa of the mouth and pharynx
was extremely difficult to treat, and severely impaired swallowing and
breathing.
The organisational aspects of treating large numbers of very ill patients
also presented significant problems. Intensive nursing care and monitoring had
to be provided 24 hours a day in small units. Personnel had to be taught new
techniques of care and patient handling, and a large number of diagnostic
samples had to be examined. The logistic requirements of medical handling
needed to be well-established before any therapeutic programme could be run
efficiently.
There were eleven deaths between 1987 and 1998 among confirmed
acute radiation sickness survivors who received doses of 1.3-5.2 Gy. There were
three cases of coronary heart disease, two cases of myelodysplasic syndrome,
two cases of liver cirrhosis, and one death each of lung gangrene, lung
tuberculosis and fat embolism. One patient, classified with Grade II, died in
1988 from acute myeloid leukaemia.
81
Radiation skin burns were observed in 56 patients. Cataracts scarring and
ulceration are the most important causes of persistent disability in acute
radiation sickness survivors.
Sexual function and fertility was investigated until 1996 in acute
radiation sickness survivors. Functional sexual disturbances predominated,
while fourteen normal children were born to acute radiation sickness survivor
families, within the first five years.
Patients with acute radiation sickness, Grades III and IV, were severely
immuno-suppressed. These abnormalities, however, are not necessarily
associated with clinically manifest immuno-deficiency.
Late health effects
There have been many reports of an increase in the incidence of some
diseases as a result of the Chernobyl accident. In fact, the accident has,
according to present knowledge, given rise to an increase in the incidence of
thyroid cancers. Also, it has had negative social and psychological
consequences. As far as other diseases are concerned, as yet the scientific
community has not been able to relate those to the effects of ionising radiation.
However, large research projects have been conducted and are under way to
further study the matter. For example, the WHO (WH95) established the
International Programme on the Health Effects of the Chernobyl Accident
(IPHECA). This programme initially concentrated on pilot projects involving
leukaemia, thyroid diseases, oral health in Belarus, mental health in children
irradiated before birth and the development of epidemiological registries. The
pilot phase came to an end in 1994 and, as a result of the findings, efforts are
underway to develop long-term permanent programmes involving thyroid
diseases, the accident recovery workers, dose reconstruction and guidance to the
public in the event of an accident. It is expected that these new projects will
provide further insight into any future health effects.
An estimate (An88) of the total lifetime cancers which could be expected
in Europe as a result of the accident suggested an increase of about 0.01%
above their natural incidence. Another assessment placed the increase in cancer
incidence at 0.004% in the Northern hemisphere, a lower percentage increase
due probably to including the large population of the whole hemisphere (Pa89).
These predictions are remarkably similar and support the view that the average
doses to the general population of the Northern hemisphere were so low that
only fractions of a percent increases in cancer incidence could be expected in
this population (Pe88, Re87). Large parts of the Northern hemisphere, such as
82
North America (Hu88, Br88), Asia and Siberia, were not significantly
contaminated and doses were inconsequential. Therefore, the following sections
focus on the late health effects in the population of the contaminated regions of
the former Soviet Union.
In the International Chernobyl Project organised by the IAEA (IA91),
field studies were undertaken in the latter half of 1990 on the permanent
residents of the rural settlements with a surface caesium contamination of
greater than 555 kBq/m
2
, and on control settlements of 2 000 to 50 000 persons,
using an age matched study design. Seven contaminated and six control
settlements were chosen by the medical team of the Chernobyl Project. Since all
persons could not be examined, representative samples were taken from various
age groups. In all, 1 356 people were examined, and the aim was to examine
about 250 from each of the larger settlements. Three medical teams each spent
two weeks conducting medical examinations to provide the data for these
assessments.
The medical examinations were quite comprehensive, and the general
conclusions reached were that there were no health abnormalities which could
be attributed to radiation exposure, but that there were significant non-radiation
related health disorders which were similar in both contaminated and control
settlements. The accident had had substantial negative social and psychological
consequences which were compounded by the socio-economic and political
changes occurring in the former Soviet Union. The official data provided to the
medical teams was incomplete and difficult to evaluate, and were not detailed
enough to exclude or confirm the possibility of an increase in the incidence of
some tumour types. On this subject, it was suggested in 1991 that the incidence
of cancer in Ukraine showed no large increase even in the most contaminated
areas (Pr91).
The International Chernobyl Project Report (IA91) suggested that the
reported high thyroid doses in some children were such that there could be a
statistically detectable increase in the incidence of future thyroid tumours. The
Chernobyl Project team finally concluded that, on the basis of the doses
estimated by the team and the currently accepted radiation risk estimates, future
increases over the natural incidence of cancer or hereditary defects would be
difficult if not impossible to discern, even with very large and well-designed
long-term epidemiological studies. However, it should be remembered that this
health survey took place four years after the accident, before any increase in
cancer incidence might be expected and reflects the status of the people
examined in a few months of 1990. The sample size was also criticised as being
too small.
83
Nevertheless, the dose estimates generally accepted indicate that, with the
exception of thyroid disease, it is unlikely that the exposure would lead to
discernible radiation effects in the general population. Many predictions of the
future impact of the accident on the health of populations have been made, all of
which, apart from thyroid disease, indicate that the overall effect will be small
when compared with the natural incidence and therefore not expected to be
discernible (An88, Be87, Hu87, Mo87, De87, Be87).
Thyroid cancer
Early in the development of the Chernobyl accident, it became obvious
that the radioiodines were contributing significant thyroid doses (Il90),
especially to children, and the then Soviet authorities made every effort not only
to minimise doses, but also to record the thyroid doses as accurately as possible.
The results of these measurements and dose reconstruction assessments
indicated that some groups in the population received high doses to their
thyroids, and that an increase in thyroid abnormalities, including cancer, was a
very real possibility in the future. This was particularly true for children in the
contaminated regions in Belarus, northern Ukraine and the Bryansk and Kaluga
regions of the Russian Federation. These were not inconsequential thyroid doses
and, as early as 1986, it was predicted by experts from the Soviet Union that the
thyroid would be the target organ most likely to show evidence of radiation
effects, especially an increased incidence of benign and malignant tumours.
It was known from previous studies of largely external irradiation of the
thyroid that an increase in thyroid tumours tended to appear six to eight years
following irradiation, and continue for more than twenty years after exposure,
particularly in children. What was not expected was that thyroid abnormalities
would already become detectable about four years after the accident. At that
time, the conventional wisdom was that internal radioiodine exposure was less
carcinogenic than external irradiation of the thyroid. Two recent studies found
an elevated risk of thyroid cancer mortality following adult
131
I treatment for
hyperthyroidim, which is in contrast to prevuious studies (Ro98, Fr99). It was
estimated that the incidence of thyroid cancers in children, defined as those
diagnosed between the ages of 0 and 14, might increase by about 5%, and in
adults by about 0.9% over the next 30 years. As will be seen, a substantial
increase has been detected in the more contaminated regions. The large number
of cases appearing within five year of the accident was surprising, since it had
been believed that thyroid cancer had a latency period of at least 10 years. A
determined effort was made to estimate doses, record the data, initiate medical
examinations and follow the cohorts already identified as being most at risk.
84
In Ukraine, more than 150 000 examinations were conducted by special
dosimetric teams, and a realistic estimate of the collective thyroid dose of
64 000 person-Sv has been made, leading to a projection of 300 additional
thyroid cancers (Li93a). In the contaminated regions of Russia, namely
Bryansk, Tula and Orel, it was predicted that an excess thyroid cancer total of
349 would appear in a population of 4.3 million (Zv93). This represents an
increase of 3 to 6% above the spontaneous rate.
A programme to monitor the thyroid status of exposed children in Belarus
was set up in Minsk in May/June 1986. The highest doses were received by the
evacuated inhabitants of the Hoiniki rayon (district) in the Gomel oblast. In the
course of this study, it was noted that the numbers of thyroid cancers in children
were increasing in some areas. For Belarus as a whole (WH90, Ka92, Wi94),
there has been a significantly increasing trend in childhood thyroid cancer
incidence since 1990 (Pa94). It was also noted that this increase is confined to
regions in the Gomel and Brest oblasts, and no significant increase has been
noted in the Mogilev, Minsk or Vitebsk areas where the radioactive iodine
contamination is assessed to have been lower. Over 50% of all the cases are
from the Gomel oblast.
For the eight years prior to 1986, only five cases of childhood (less than
15 years old on the day of accident) thyroid cancer were seen in Minsk, which is
the main Belarussian centre for thyroid cancer diagnosis and treatment for
children (De94). From 1986 to 1989, 3 to 6 cases of thyroid cancer in children
were seen annually in Belarus. In 1990, the number jumped to 31, to 62 in 1991,
then to 87 in 1993. By the end of 1998 the total had reached over 600 in
Belarus. Nearly 50% of the early (1992) thyroid cancers appeared in children
who were aged between one and four years at the time of the accident. Atthe
same time 382 were diagnosed in the Ukraine.
The histology of the cancers has shown that nearly all were papillary
carcinomata (Ni94) and that they were particularly aggressive, often with
prominent local invasion and distant metastases, usually to the lungs. This has
made the treatment of these children less successful than expected, whether
undertaken in Minsk or in specialised centres in Europe. In all, about
150 000 children in Belarus had thyroid uptake measurements following the
accident. Other data from Ukraine and Russia show a similar, but not as
pronounced, increase in the incidence of childhood thyroid cancer since 1987.
The increase in Belarus was confirmed by the final report of an EC
Expert Panel (EC93) convened in 1992 to investigate the reported increase. In
1992 the incidence of childhood thyroid cancer in Belarus as a whole was
estimated to be 2.77 per 100 000, more recent information (Un00) raises the
85
incidence in 1992 to 3.9 per 100 000, whereas in the Gomel and Brest oblasts it
was 11.2 and 3.7 respectively. In Belarus, it was observed that children
0-4 years old at the time of accident still had an increase in absolute numbers of
thyroid cancers in 1997, while the number of cancers among those who were
5-9 years old seem to decrease after 1995, in those of 10-14 years of age at
exposure, the number of cancers seems to be stable for the period 91-97 (Ko99).
There is some difficulty in comparing the numbers quoted by the health
authorities of the former Soviet Union with previous incidence statistics, as
previous data collection was not sufficiently rigorous. Moreover, the absolute
numbers can differ from one report to another, and the age scale taken into
consideration can differ between 0-14, 0-17 or 0-18 years of age. However, in
Belarus all cases of childhood thyroid cancer have been confirmed since 1986
by international review of the histology and, because of more rigid criteria for
data collection, reliance can be placed on accuracy and completeness. An
attempt to review incidence estimates was made in the above-mentioned EC
Report (EC93). These experts confirmed that the incidence of childhood thyroid
cancer (0-14 y) prior to the accident in Belarus (between 0 and 0.14/100 000/y)
was similar to that reported by other cancer registries. This indicates that the
data collection in Belarus was adequate. They noted that it jumped to
3.9/100 000/y in 1991, and 5.6/100 000 in 1995 and 1997, about a forty-fold
increase.
The most recent published rates of childhood thyroid cancer (St95) show
unequivocal increases as seen in Table 13. At the time of this writing, three of
the 1036 children cited in Table 13 below have died of their disease.
Table 13. Number of cases of thyroid cancers in children under 15 years old
at diagnosis and cancer incidence rates number of cases
per 100 000 children
86 87 88 89 90 91 92 93 94 95 96 97 98
Belarus 3
0.2
4
0.3
6
0.4
5
0.3
31
1.9
62
3.9
62
3.9
87
5.5
77
5.1
82
5.6
67
4.8
73
5.6
48
3.9
Russian
Federation
– 1
0.3
– – 1
0.3
1
0.3
3
0.9
1
0.3
6
2.8
7
2.5
2
0.6
5
2.2
–
Ukraine 8
0.2
7
0.1
8
0.1
11
0.1
26
0.2
22
0.2
49
0.5
44
0.4
44
0.4
47
0.5
56
0.6
36
0.4
44
0.5
Total 11 12 14 16 58 85 114 132 127 136 125 114 92
86
When this increase was first reported, it was very quickly pointed out
(Be92) that any medical surveillance programme introduced would apparently
increase the incidence by revealing occult disease and rectifying misdiagnoses.
While this may account for some of the increase (Ro92), it cannot possibly be
the sole cause, as the increase is so large and many of the children presented not
with occult disease, but with clinical evidence of thyroid and/or metastatic
disease. In fact, only 12% of the childhood thyroid cancers were discovered by
ultrasound screening alone in Belarus (WH95). In addition, subsequent
examination by serial section of the thyroids of persons coming to autopsy in
Belarus have confirmed that the number of occult thyroid cancers is similar to
that found in other studies (Fu93) and showed none of the aggressive
characteristics found in the childhood cancers presenting in life (Fu92).
It can be concluded that there is a real, and large, increase in the
incidence of childhood thyroid cancer in Belarus and Ukraine which is likely to
be related to the Chernobyl accident. This is suggested by features of the
disease, which differ somewhat from the so-called natural occurrence, as well as
by its temporal and geographic distribution.
As far as other thyroid disorders are concerned, no difference in Russia
was detected by ultrasound examination, in the percentage incidence of cysts,
nodules or autoimmune thyroiditis in the contaminated versus the un-
contaminated areas (Ts94). Following the accident, children in the Ukrainian
contaminated regions exhibited a transient dose-dependent increase in serum
thyroxine level, without overt clinical thyrotoxicosis, which returned to normal
within 12 to 18 months (Ni94). This was most marked in the youngest children.
This finding cannot be regarded as an adverse health effect, as no abnormality
was permanent. However, it may be a pointer to future thyroid disease,
especially when it may be associated with mild regional dietary iodine
deficiency, and indicates the need for continued monitoring.
This increased incidence was not confined to children, as a larger number
of adult cases was registered in Belarus and in Ukraine (WH94). In a more
recent report (Iv99) 3 082 thyroid cancer cases in persons less than 60 years of
age at diagnosis were recorded in Russian Federation between 1982 and 1996 in
the four most contaminated regions. Among those 0-17 years of age at time of
the accident, 178 cases were found. In the same report we can observe that
before the accident, the incidence of cancer in women in these contaminated
areas was lower than the national incidence in the Russian federation for the
period 1982-1986, but increased.
For the period of 12 years after the Chernobyl accident, thyroid
carcinoma increased by 4 057 cases in Belarus, as compared to the same period
87
of time before. Since 1974 to 1985 thyroid carcinomas developed in
1 392 patients, but from 1986 up to July 1998, 5 449 new cases were diagnosed
(De99). The standard index reached 7.9 per 100 000 in population above
18 years old and 3-4 per 100 000 in children. Thyroid carcinomas were mainly
diagnosed in children born before the accident. Once all
131
I had disintegrated,
spontaneous carcinomas were diagnosed only in six children born in 1987 and
1988. Since 1996, the number of child patients has gradually decreased, while
the incidence rates in adults continue to increase. We can expect during the
second decade after the accident a peek of incidence for young people at age
from 15 to 34 at the time of the accident. Among children and teenagers (age
0-18 at the time of the Chernobyl accident) we observe among thyroid cancers a
mortality of 0.7% (observed time – 1986-2001) (Ke01).
An analysis of thyroid cancers in children and adolescents of the Ukraine
(0-18 years of age at the time of surgery) showed that for period 1986 to 1997,
577 cases were registered (Tr99). Among 358 cases in children (0-14 years of
age at time of surgery), the incidence per 100 000 children for the whole of the
Ukraine has increased from 0.05 before the accident to 0.11 in 1986-1990, 0.39
in 1991-1995, and 0.44 in 1996-1997. The increase of incidence takes place
mainly in children who were 5-years old or less in 1986.
Jacob et al reported a correlation between collective dose and incidence
of thyroid cancers in 5 821 settlements in the three republics in 1991-1995.
Using the southern half of Ukraine as a reference, the excess thyroid cancers
risk was found to be linear in the dose interval 0.07 Gy to 1.2 Gy. For the
0-18 years of age group, Jacob et al obtain an excess absolute risk of 2.1 per
104 person-year Gy (Je98). In this study the authors did not relate any age (at
exposure)-dependence for excess absolute risk for the birth cohort 1968-1985
(Je99) in contradiction with the Trosko report (Tr99) and the Japanese
observations within the framework of the Sasakawa project in Belarus (Sh98).
In another study, Ivanov et al (Iv99) reported excess absolute risk for children
and adolescents comparable to those described by Jacob et al, 2.21 per
104 person-year Gy for girls and 1.62 for boys, described also a dose-risk linear
relationship, but observed a dependence of risk with age at exposure, 14 times
higher than in adults than for 0-4 years, 2.3 for children and adolescents.
The radiogenic nature of these thyroid tumours is supported by their
relationship with thyroid exposure dose, clinical and morphological changes,
aggressiveness of cancers, geostatistical studies (Bl97). This is in spite of the
increase of ultrasound screening, which can explain a part of the increase in
observed cases. However certain uncertainties remain, such as iodine deficiency
and genetic predisposition, as well as the role of
131
I. For example, it has been
suggested that the geographical distribution of thyroid cancers cases correlates
88
better to the distribution of short-lived radioisotopes (
132
I,
133
I and
135
I) than to
that of
131
I (Av95).
Table 14. Thyroid cancers and risk for children 0-18 years old at the time
of the Chernobyl accident for the years 1991-1995 in three cities
and 2 729 settlements in Belarus and the Russian Federation
Thyroid dose Person
years at risk
Observed
number of
cases
Expected
number of
cases
a
Exsess absolute
risk
b
(10
4
PY Gy)
-1
0-0.1 (0.05)
0.1-0.5 (0.21)
0.5-1.0 (0.68)
1.0-2.0 (1.4)
>2.0 (3.0)
1 756 000
1 398 000
386 000
158 000
56 000
38
65
52
50
38
16
13
3.6
1.5
0.5
2.6 (0.5-6.7)
1.9 (0.8-4.1)
2.0 (0.9-4.2)
2.3 (1.1-4.9)
2.4 (1.1-5.1)
a) Calculated by multiplying the age-specific incidence observed in Belarus in 1983-1987
by three.
b) 95% confidence intervals in parentheses.
Credit: Sources and Effects of Ionising Radiation – United Nations Scientific committee on the
Effects of Atomic Radiation – UNSCEAR 2000 report to the General Assembly with Scientific
Annexes – Volume II: Effects, United Nations.
In the six most contaminated regions of the Russian Federation, the
thyroid cancer incidence increased over time in adults. The incidence was
11 per 100 000 for women compared to 4 for the Russian Federation as a whole
and 1.7 and 1.1 respectively for men.
In a study of Lithuanian recovery operation workers, three thyroid
cancers were detected. There was no significant difference compared with the
Lithuanian male population and no association with level of radiation dose or
duration of stay in the area of Chernobyl. In Europe, where several studies were
carried out, no increase of thyroid cancer among children was observed.
The majority of the estimates indicate that the overall health impact from
these thyroid disorders will be extremely small and not detectable when
averaged over the population potentially at risk. This viewpoint is widely held
by the competent risk assessors who have examined the potential effects of the
accident.
89
Other late health effects
From data in the Russian National Medical Dosimetric Registry
(RNMDR), the reported incidence of all types of disease has risen between
1989 and 1992 (Iv94). There has also been a reported increase in malignant
disease which might be due to better surveillance and/or radiation exposure. The
crude mortality rate of the liquidators from all causes in the Russian Federation
has increased from 5 per 1 000 in 1991 to 7 per 1 000 in 1992. The crude death
rate from respiratory cancer is reported to have increased significantly between
1990 and 1991, and for all malignant neoplasms between 1991 and 1992. It is
not clear what influence smoking has had on these data, and the overall
significance of these findings will need to be established by further surveillance,
especially when there are distinct regional variations in the crude death rate and
the mortality rates from lung, breast and intestinal cancer are rising in the
general population of the Russian Federation.
From the dosimetric data in the RNMDR (Iv94), a predicted excess
670 cancer deaths may occur in the exposed groups covered by the Registry,
peaking in about 25 years. This is about 3.4% of the expected cancer deaths
from other causes. Data from the other national dose registries is not readily
available in the published literature.
In view of the difficulties associated with these Registry data, such as the
dose estimates, the influence of such confounding factors as smoking, the
difficulty in follow-up, the possible increase in some diseases in the general
population and also the short time since the accident, it is not possible to draw
any firm conclusions from these data at this time. The only inference that can be
made is that these groups are the most exposed and that, if any radiation effects
are to be seen, they will occur in selected cohorts within these registries, which
will require long-term future surveillance.
A predicted increase of genetic effects in the next two generations was
0.015% of the spontaneous rate, and the estimated lifetime excess percentage of
all cancers as a result of living in the strict control zones was 0.5%, provided
that a lifetime dose limit of 350 mSv was not exceeded (Il90).
Childhood leukemia incidence has not changed in the decade since the
accident. There is no significant change in the level of leukemia and related
diseases in the contaminated (more than 555 kBq/m
2
) and noncontaminated
territories of the three states (WH95). Other attempts through epidemiological
studies have failed to establish a link between radiation exposure from the
Chernobyl accident and the incidence of leukemia and other abnormalities. No
epidemiological evidence of an increase in childhood leukemia around
90
Chernobyl (Iv93, Iv 97), in Sweden (Hj94, To96), Germany (Mi97) or the rest
of Europe (Pa92, Wi94) has been established. However, if the last OECD/NEA
report recommended to be prudent, to withold final judgement, 6years later, no
increased risk of leukemia related to ionising radiation has as yet been found
among recovery operation workers. The probability of observing a significant
increase of leukemias decreases with time, and the next five years will be
conclusive.
Other studies
Various reports (Pa93, Sc93, Se95, St93, Ve93) have been published on
the incidence of chromosome aberrations among people exposed both in the
contaminated regions and in Europe. Some of these have shown little or no
increase, while others have. This may reflect the wide variation in dose.
However, there is a trend for the incidence of chromosome aberrations to return
to normal with the passage of time. Other studies have not shown evidence of
lymphocytic chromosome damage (Br92).
In East Germany one study found no rise in foetal chromosome
aberrations between May and December 1986. Chromosome aberrations are to
be expected in any exposed population, and should be regarded as biological
evidence of that exposure, rather than an adverse health effect.
Another study in Germany suggesting a link between Down’s syndrome
(Trisomy 21) and the Chernobyl accident has been severely criticised and
cannot be accepted at face value because of the absence of control for
confounding factors (Sp91), and it was not confirmed by more extensive studies
(Li93). Another study in Finland (Ha92) showed no association of the incidence
of Trisomy 21 with radiation exposure from Chernobyl.
In a group of Belarussian children born to exposed mothers with in utero
doses ranging from 8 to 21 mSv, no relationship between birth defects and
residency in contaminated areas was seen (La90). At this time, no clear trends
in data for birth anomalies in Belarus or Ukraine be established (Li93, Bo94).
Later study of Lazuk et al. has shown increase of birth defects and
malformations in contaminated areas (1997), but no changes could be related to
exposure to ionising radiation since the same increase was observed in the city
of Minsk used as control.
Two epidemiological studies in Norway concluded that no serious gross
changes as to pregnancy outcome were observed (Ir91), and that no birth
defects known to be associated with radiation exposure were detected (Li92). In
91
Austria, no significant changes in the incidence of birth defects or spontaneous
abortion rates which could be attributed to the Chernobyl accident were
detected (Ha92a).
A review by the International Agency for Research on Cancer (IARC)
showed no consistent evidence of a detrimental physical effect of the Chernobyl
accident on congenital abnormalities or pregnancy outcomes (Li93, EG88). No
reliable data have shown any significant association between adverse pregnancy
outcome or birth anomalies even in the most contaminated regions and the
doses indicate that none would be expected.
On the basis of many studies, UNSCEAR in its last report (UN00)
conclude that “no increase in birth defects, congenital malformations, stillbirths,
or premature births could be linked to radiation exposures caused by the
accident”.
No association between thyroid abnormalities and
137
Cs activity in the
body or soil contamination was seen in 115 000 children in the Sasakawa
framework health and Medical cooperation project (Ya97).
There have been reports that have suggested that radiation exposure as a
result of the accident resulted in altered immune reactions. While immune
suppression at high whole-body doses is known to be inevitable and severe, at
the low doses experienced by the general population it is expected that any
detected alterations will be minor and corrected naturally without any medical
consequences. These minor changes may be indicative of radiation exposure,
but their mild transitory nature is unlikely to lead to permanent damage to the
immune system. All immunological tests of radiation exposure are in their
infancy, but tests such as stimulated immunoglobulin production by
lymphocytes hold promise for the future as a means of assessing doses below
one Gy (De90).
Psychological and social health effects
One of the most significant effects of the Chernobyl accident has been the
degridation of the social fabric in the affected territories. This has, it is felt
(UN02), contributed to a general decline in well being through an increase in
health effects that are related to the accident, but which are not necessarily
radiation related. That is, the non-cancer health effects that are currently being
studied seem not to result directly from irradiation, but from the stresses
(physical and psychological) that have persisted since the accident.
92
In addition, the severity of the psychological effects of the Chernobyl
accident appears also to be related to the public’s growing mistrust of
officialdom, politicians and government, especially in the field of nuclear
power. Public scepticism towards authority is reinforced by its difficulty in
understanding radiation and its effects, as well as the inability of the experts to
present the issues in a way that is comprehensible. The impression that an
unseen, unknowable, polluting hazard has been imposed upon them by the
authorities against their will, fosters a feeling of outrage.
Public outrage is magnified by the concept that their existing or future
descendants are also at risk from this radiation pollution. This widespread
public attitude was not confined to one country, and largely determined the
initial public response outside the Soviet Union. The public distrust was
increased by the fact that the accident that they had been told could not happen,
did happen, and it induced anxiety and stress in people not only in the
contaminated areas but, to a lesser extent, all over the world.
While stress and anxiety cannot be regarded as direct physical adverse
health effects of irradiation, their influence on the well-being of people who
were exposed or thought that they might have been, may well have a significant
impact on the exposed population. Several surveys have shown that the
intensity of the anxiety and stress are directly related to the presence of
contamination. It should also be remembered that the stress induced by the
radiological contamination caused by the accident was in addition to that
produced in the general population by the upheaval in local social structures due
to massive evacuation and relocations, and the severe economic and social
hardship caused by the break-up of the Soviet Union.
These non-radiological effects related to the Chernobyl accident have
been studied extensively. Symptoms such as headaches, depression, sleep
disturbance, inability to concentrate, and emotional imbalance have been
reported and seen to be related to the difficult conditions ands stressful events
that followed the accident (Le96, Le96a). The psychological development of
138 belarussian children who were exposed in utero was compared with
122 children from non contaminated areas. A correlation was found between
anxiety among parents and emotional stress in children; No differences could be
related to ionising radiation (Ko99).
It was concluded that the Chernobyl accident has had a significant long-
term impact on psychological well-being, health-related quality of life, and
illness in the affected populations. However, none of these findings could be
directly associated with ionising radiation (Ha97, UN00).
93
Within the former Soviet Union
Within the Soviet Union additional factors came into play to influence the
public reaction. It should be remembered that this accident occurred during the
initial period of “glasnost” and “perestroika”. After nearly seventy years of
repression, the ordinary people in the Soviet Union were beginning openly to
express all the dissatisfaction and frustration that they had been harbouring.
Distrust and hatred of the central government and the Communist system could
be expressed for the first time without too much fear of reprisal. In addition,
nationalism was not repressed. The Chernobyl accident appeared to epitomise
everything that was wrong with the old system, such as secrecy, witholding
information and a heavy-handed authoritarian approach. Opposition to
Chernobyl came to symbolise not only anti-nuclear and anti-communist
sentiment but also was associated with an upsurge in nationalism.
The distrust of officialdom was so great that even scientists from the
central government were not believed, and more reliance was placed on local
“experts” who often had very little expertise in radiation and its effects. The
then Soviet Government recognised this problem quickly, and tried to
counteract the trend by inviting foreign experts to visit the contaminated areas,
assess the problems, meet with local specialists and publicise their views in
open meetings and on television. These visits appeared to have a positive effect,
at least initially, in allaying the fears of the public. In the contaminated
Republics, anxiety and stress were much more prevalent and were not just
confined to the more heavily contaminated regions (WH90a). Several surveys
conducted by Soviet (Al89) and other researchers (Du94) have shown that the
anxiety induced by the accident has spread far beyond the more heavily
contaminated regions.
During this period there was severe economic hardship which added to
the social unrest and reinforced opposition to the official system of government.
Anti-nuclear demonstrations were commonplace in the larger cities in Belarus
(Gomel and Minsk), and Ukraine (Kiev and Lvov) in the years following the
accident (Co92). The dismissive attitude of some Soviet scientists and
government officials in describing the public reaction as “radiophobic” tended
to alienate the public even further by implying some sort of mental illness or
reaction which was irrational and abnormal. It also served as a convenient
catch-all diagnosis which suggested that the public was somehow at fault, and
the authorities were unable to do anything about its manifestations.
The concern of people for their own health is only overshadowed by their
concern for the health of their children and grandchildren. Major and minor
health problems are attributed to radiation exposure no matter what their origin,
94
and the impact that the accident has had on their daily lives has added to the
stress. Whole communities are facing or have faced evacuation or relocation.
There are still widespread restrictions on daily life affecting schooling, work,
diet and recreation.
The accident has caused disruption of social networks and traditional
ways of life. As most inhabitants of the contaminated settlements are native to
the area and often have lived there all their lives, relocation has in many cases,
destroyed the existing family and community social networks, transferring
groups to new areas where they may well be resented or even ostracised. In
spite of these drawbacks, about 70% of the people living in contaminated areas
wished to be relocated (IA91). This may well be influenced by the economic
incentives and improved living standards that result from relocation by the
government.
There are two additional circumstances and events which have tended to
increase the psychological impact of the accident, the first of which was an
initiative specifically designed to alleviate these effects in Ukraine. This was the
introduction of the compensation law in Ukraine in 1991. Some three million
Ukrainians were affected in some way by the post-accident management
introduced, upon which approximately one sixth of the total national budget
was spent (Du94). Different surveys have shown a general feeling of anxiety in
all sectors of the population, but it was particularly acute among those who had
been relocated. People were fearful of what the future might bring for
themselves and their offspring, and were concerned about their lack of control
over their own destiny.
The problem is that the system of compensation may well have
exaggerated these fears by placing the recipients into the category of victims.
This tended to segregate them socially and increased the resentment of the
native population into whose social system these “victims” had been injected
without consultation. This had the effect on the evacuees of increasing stress,
often leading to withdrawal, apathy and despair. Locally, this compensation was
often referred as a “coffin subsidy”! It is interesting to note that the 800 or so
mostly elderly people who have returned to their contaminated homes in the
evacuated zones, and hence receive no compensation, appear to be less stressed
and anxious, in spite of worse living conditions, than those who were relocated.
It should be pointed out that compensation and assistance are not harmful in
themselves, provided that care is taken not to induce an attitude of dependence
and resignation in the recipients.
The second factor which served to augment the psychological impact of
the accident was the acceptance by physicians and the public of the disease
95
entity known as “vegetative dystonia”. This diagnosis is characterised by vague
symptoms and no definitive diagnostic tests. At any one time, up to
1 000 children were hospitalised in Kiev, often for weeks, for treatment of this
“disease” (St92). The diagnosis of vegetative dystonia appears to be tailor-made
for the post-accident situation, assigned by parents and doctors to account for
childhood complaints and accepted by adults as an explanation for vague
symptoms.
There is great pressure on the physicians to respond to their patients’
needs in terms of arriving at an acceptable diagnosis, and “Vegetative Dystonia”
is very convenient as it will fit any array of symptoms. Such a diagnosis not
only justifies the patients’ complaints by placing the blame for this “disease” on
radiation exposure, it also exonerates the patient from any responsibility, which
is placed squarely on the shoulders of those responsible for the exposure – the
Government. When the need for extended hospitalisation is added, the
justification to accept this as a real disease is enhanced. It can be understood
why there is an epidemic of this diagnosis in the contaminated areas.
Outside the former Soviet Union
Social and psychological effects in other countries were minimal
compared with those within the former Soviet Union, and were generally
exhibited more as concerned social reactions rather than health symptoms. In
the contaminated regions of the former Soviet Union, many people were
convinced that they were suffering from radiation induced disease, whereas in
the rest of the world, where contamination was much less, news of the accident
appeared to reinforce anti-nuclear perceptions in the general population. This
was evidenced, for example, by the demonstrations on 7 June 1986 demanding
the decommissioning of all nuclear power plants in the Federal Republic of
Germany (Ze86). While in France public support for nuclear power expansion
dropped since the accident, 63% of the population felt that French nuclear
power reactors operated efficiently (Ch90). The minimal impact of the
Chernobyl accident on French public opinion was probably due to the fact that
about 75% of their electrical power is derived from nuclear stations, and in
addition, France was one of the least contaminated European countries.
The Swedish public response has been well-documented (Dr93, Sj87). In
the survey, the question was asked: “With the experience that we now have, do
you think it was good or bad for the country to invest in Nuclear Energy?”
Those that responded “bad” jumped from 25% before, to 47% after Chernobyl.
The accident probably doubled the number of people who admitted negative
attitudes towards nuclear power (Sj87). This change was most marked among
96
women, who, it was felt, regarded nuclear power as an environmental problem,
whereas men regarded it as a technical problem which could be solved. Media
criticism of the radiation protection authorities in that country became more
common, with the charge that the official pronouncements on the one hand said
that the risk in Sweden was negligible, and yet on the other, gave instructions
on how it could be reduced. The concept that a dose, however small, should be
avoided if it could be done easily and cheaply, was not understood.
This sort of reaction was common outside the former Soviet Union, and
while it did not give rise to significant health effects, it tended to enhance public
apprehension about the dangers of nuclear power and foster the public’s
growing mistrust of official bodies.
In addition, public opinion in Europe was very sceptical of the
information released by the Soviet Union. This mistrust was reinforced further
by the fact that the traditional sources of information to which the public tended
to turn in a crisis, the physicians and teachers, were no better informed and
often only repeated and reinforced the fears that had been expressed to them.
Added to this were the media, who tended to respond to the need to print
“newsworthy” items by publishing some of the more outlandish claims of so-
called radiation effects.
The general public was confused and cynical and responded in
predictable but extreme ways such as seeking induced abortions, postponing
travel and not buying food that might conceivably be contaminated. Another
global concern that was manifested, was the apprehension over travel to the
Soviet Union. Potential travellers sought advice from national authorities on
whether to travel, what precautions to take and how they could check on their
exposure. Many people, in spite of being reassured that it was safe to travel,
cancelled their trip, just to be on the safe side, exhibiting their lack of
confidence in the advice they received.
As has been seen, governments themselves were not immune from the
influence of these fears and some responded by introducing measures such as
unnecessarily stringent intervention levels for the control of radionuclides in
imported food. Thus, in the world as a whole, while the effects on individuals,
due to anxiety and stress, were probably minimal, the collective perception and
response had a significant economic and social impact. It became clear that
there was a need to inform the public on radiation effects, to provide clear
instructions on the precautions to be taken so that the public regains some level
of personal control, and for the authorities to recognise the public’s need to be
involved in the decisions that affect them.
97
In summary
It can be stated that:
• Thirty-one people died in the course of the accident or soon after and
another 134 were treated for the acute radiation syndrome. Forty-one
of these patients received whole-body doses from external
irradiation of less than 2.1 Gy, 2& between 6.5 and 16 Gy.
• Extensive accident-related health effects are apparent in the affected
regions of the former Soviet Union, manifested as anxiety and stress,
as well as diverse health effects not directly related to radiation
exposure. Severe forms induce a feeling of apathy and despair often
leading to withdrawal. In the rest of the world these individual
effects were minimal.
• In the last decade, there has been a real and significant increase in
childhood and, to a certain extent, adult carcinoma of the thyroid in
contaminated regions of the former Soviet Union (Wi940) which
should be attributed to the Chernobyl accident until proven
otherwise.
• In children, the thyroid cancers are:
− largely papillary and particularly aggressive in nature often self
presenting with local invasion and/or distant metastases;
− more prevalent in children aged 0 to 5 years at the time of the
accident, and in areas assessed to be the more heavily
contaminated with
131
I;
− apparently characterised by a shorter latent period than
expected; and
− still increasing for children younger than 5 years in 1986.
Iodine deficiency and screening, have almost certainly had an influence
on observed risk factors can be said that the increase of thyroid cancers in
children is clearly established to be linked to exposure of radioactive iodine
isotopes releases. The number of these cancers is still increasing in adults.
Conversely, no increase in leukaemia has been observed to date.
No increase of congenital abnormalities, adverse pregnancy outcomes or
any other radiation induced disease in the general population, either in the
contaminated regions or in Western Europe, could be attributed to this exposure
sixteen years after the accident. It is unlikely that surveillance of the general
population will reveal any significant increase in the incidence of cancer but
98
continued follow-up is necessary to allow planning of public health actions and
to gain a better understanding of influencing factors.
The present knowledge of the effects of protracted exposure to ionising
radiations is limited, since the dose-assessments rely heavily on high-dose
exposure. An increase in cancer rates was already observed before the
Chernobyl accident in the affected areas and, moreover, a general increase in
mortality has been reported in recent years in most areas of the former USSR.
Among recovery operation workers, no increase of leukaemia has been
identified more than sixteen years after the accident.
Among the health consequences resulting from the Chernobyl accident,
are radiological consequences, and other, non-radiological health problems.
The radiological aspects have been studied in great detail since the accident, and
have been well characterised, within the limits of scientific uncertainty of
radiological sciences. However, increasingly, medical specialists are studying
other health effects that are not associated with radiation exposure, but more
with the effects of significant and prolonged stress, physical and psychological.
These effects, which have been classified as “Vegetative Dystonia”, are
increasingly recognised as real, but are felt to result from the social, cultural and
psychological stress caused by the accident and the general social degradation
that followed the accident and the end of the Soviet Union. To obtain a more
exact understanding of these “accident-related effects”, it is important to expand
current studies to include specialists from studies of the health and social effects
of other natural and technological disasters.
99
Chapter VI
AGRICULTURAL AND ENVIRONMENTAL IMPACTS
Agricultural impact
All soil used anywhere in the world for agriculture contains radionuclides
to a greater or lesser extent. Typical soils (IA89a) contain approximately
300 kBq/m
3
of
40
K to a depth of 20 cm. This radionuclide and others are then
taken up by crops and transferred to food, leading to a concentration in food and
feed of between 50 and 150 Bq/kg. The ingestion of radionuclides in food is one
of the pathways leading to internal retention and contributes to human exposure
from natural and man-made sources. Excessive contamination of agricultural
land, such as may occur in a severe accident, can lead to unacceptable levels of
radionuclides in food.
The radionuclide contaminants of most significance in agriculture are
those which are relatively highly taken up by crops, have high rates of transfer
to animal products such as milk and meat, and have relatively long radiological
half-lives. However, the ecological pathways leading to crop contamination and
the radioecological behaviour of the radionuclides are complex and are affected
not only by the physical and chemical properties of the radionuclides but also
by factors which include soil type, cropping system (including tillage), climate,
season and, where relevant, biological half-life within animals. The major
radionuclides of concern in agriculture following a large reactor accident are
131
I,
137
Cs,
134
Cs and
90
Sr (IA89a). Direct deposition on plants is the major
source of contamination of agricultural produce in temperate regions.
While the caesium isotopes and
90
Sr are relatively immobile in soil,
uptake of roots is of less importance compared with plant deposition. However,
soil type (particularly with regard to clay mineral composition and organic
matter content), tillage practice and climate all affect propensity to move to
groundwater. The same factors affect availability to plants insofar as they
control concentrations in soil solution. In addition, because caesium and
strontium are taken up by plants by the same mechanism as potassium and
100
calcium respectively, the extent of their uptake depends on the availability of
these elements. Thus, high levels of potassium fertilisation can reduce caesium
uptake and liming can reduce strontium uptake.
Within the former Soviet Union
The releases during the Chernobyl accident contaminated about
125 000 km
2
of land in Belarus, Ukraine and Russia with radiocaesium levels
greater than 37 kBq/m
2
, and about 30 000 km
2
with radiostrontium greater than
10 kBq/m
2
. About 52 000 km
2
of this total were in agricultural use; the
remainder was forest, water bodies and urban centres (Ri95). While the
migration downwards of caesium in the soil is generally slow (Bo93), especially
in forests and peaty soil, it is extremely variable depending on many factors
such as the soil type, pH, rainfall and agricultural tilling. The radionuclides are
generally confined to particles with a matrix of uranium dioxide, graphite, iron-
ceramic alloys, silicate-rare earth, and silicate combinations of these materials.
The movement of these radionuclides in the soil not only depends on the soil
characteristics but also on the chemical breakdown of these complexes by
oxidation to release more mobile forms. The bulk of the fission products is
distributed between organomineral and mineral parts of the soil largely in humic
complexes. The 30-km exclusion zone has improved significantly partly due to
natural processes and partly due to decontamination measures introduced.
There were also large variations in the deposition levels. During 1991 the
137
Cs activity concentrations in the 0-5 cm soil layer ranged from 25 to
1 000 kBq/m
3
and were higher in natural than ploughed pastures. For all soils,
between 60 and 95% of all
137
Cs was found to be strongly bound to soil
components (Sa94). Ordinary ploughing disperses the radionuclides more
evenly through the soil profile, reducing the activity concentration in the 0-5 cm
layer and crop root uptake. However, it does spread the contamination
throughout the soil, and the removal and disposal of the uppermost topsoil may
well be a viable decontamination strategy.
The problem in the early phase of an accident is that the countermeasures
designed to avoid human exposure are of a restrictive nature and often have to
be imposed immediately, even before the levels of contamination are actually
measured and known. These measures include the cessation of field work, of the
consumption of fresh vegetables, of the pasturing of animals and poultry, and
also the introduction of uncontaminated forage. Unfortunately, these measures
were not introduced immediately and enhanced the doses to humans in
Ukraine (Pr95).
101
Furthermore, some initial extreme measures were introduced in the first
few days of the accident when 15 000 cows were slaughtered in Ukraine
irrespective of their level of contamination, when the introduction of clean
fodder could have minimised the incorporation of radiocaesium. Other counter-
measures, such as the use of potassium fertilisers, decreased the uptake of
radiocaesium by a factor of 2 to 14, as well as increased crop yield.
In some podzolic soils, lime in combination with manure and mineral
fertilisers can reduce the accumulation of radiocaesium in some cereals and
legumes by a factor of thirty. In peaty soils, sand and clay application can
reduce the transfer of radiocaesium to plants by fixing it more firmly in the soil.
The radiocaesium content of cattle for human consumption can be minimised by
a staged introduction of clean feed during about ten weeks prior to slaughter. A
policy of allocating critical food production to the least contaminated areas may
be an effective common sense measure.
In 1993, the concentration of
137
Cs in the meat of cows from the Kolkhoz
in the Sarny region, where countermeasures could be implemented effectively,
tended to be much lower than that in the meat from private farms in the
Dubritsva region (Pr95). The meat of wild animals which could not be subjected
to the same countermeasures had a generally high concentration of radio-
caesium. Decontamination of animals by the use of Prussian Blue boli was
found to be very effective where radiocaesium content of feed is high and where
it may be difficult to introduce clean fodder (Al93). Depending on the local
circumstances, many of the above mentioned agricultural countermeasures were
introduced to reduce human exposure.
Since July 1986, the dose rate from external irradiation in some areas has
decreased by a factor of forty, and in some places, it is less than 1% of its
original value. Nevertheless, soil contamination with
137
Cs,
90
Sr and
239
Pu is still
high and in Belarus, the most widely contaminated Republic, eight years after
the accident 2 640 km
2
of agricultural land had been excluded from use (Be94).
Within a 40-km radius of the power plant, 2 100 km
2
of land in the Poles’e state
nature reserve have been excluded from use for an indefinite duration.
The uptake of plutonium from soil to plant parts lying above ground
generally constitutes a small health hazard to the population from the ingestion
of vegetables. It only becomes a problem in areas of high contamination where
root vegetables are consumed, especially if they are not washed and peeled. The
total content of the major radioactive contaminants in the 30-km zone has been
estimated at 4.4 PBq for
137
Cs, 4 PBq for
90
Sr and 32 TBq for
239
Pu and
240
Pu.
102
However, it is not possible to predict the rate of reduction as this is
dependent on so many variable factors, so that restrictions on the use of land are
still necessary in the more contaminated regions in Belarus, Ukraine and Russia.
In these areas, no lifting of restrictions is likely in the foreseeable future. It is
not clear whether return to the 30 km exclusion zone will ever be possible, nor
whether it would be feasible to utilise this land in other ways such as grazing for
stud animals or hydroponic farming (Al93). It is however, to be recognised that
a small number of generally elderly residents have returned to that area with the
unofficial tolerance of the authorities.
Within Europe
In Europe, a similar variation in the downward migration of
137
Cs has
been seen, from tightly bound for years in the near-surface layer in meadows
(Bo93), to a relatively rapid downward migration in sandy or marshy areas
(EC94). For example, Caslano (TI) experienced the greatest deposition in
Switzerland and the soil there has fallen to 42% of the initial
137
Cs content in the
six years after the accident, demonstrating the slow downward movement of
caesium in soil (OF93). There, the
137
Cs from the accident has not penetrated to
a depth of more than 10 cm, whereas the contribution from atmospheric nuclear
weapon tests has reached 30 cm of depth.
In the United Kingdom, restrictions were placed on the movement and
slaughter of 4.25 million sheep in areas in southwest Scotland, northeast
England, north Wales and northern Ireland. This was due largely to root uptake
of relatively mobile caesium from peaty soil, but the area affected and the
number of sheep rejected are reducing, so that, by January 1994, some
438 000 sheep were still restricted. In northeast Scotland (Ma89), where lambs
grazed on contaminated pasture, their activity decreased to about 13% of the
initial values after 115 days; where animals consumed uncontaminated feed, it
fell to about 3.5%. Restrictions on slaughter and distribution of sheep and
reindeer, also, are still in force in some Nordic countries.
The regional average levels of
137
Cs in the diet of European Union
citizens, which was the main source of exposure after the early phase of the
accident, have been falling so that, by the end of 1990, they were approaching
pre-accident levels (EC94). In Belgium, the average body burden of
137
Cs
measured in adult males increased after May 1986 and reached a peak in late
1987, more than a year after the accident. This reflected the ingestion of
contaminated food. The measured ecological half-life was about 13 months. A
similar trend was reported in Austria (Ha91).
103
In short, there is a continuous, if slow, reduction in the level of mainly
137
Cs activity in agricultural soil.
Environmental impact
Forests
Forests are highly diverse ecosystems whose flora and fauna depend on a
complex relationship with each other as well as with climate, soil characteristics
and topography. They may be not only a site of recreational activity, but also a
place of work and a source of food. Wild game, berries and mushrooms are a
supplementary source of food for many inhabitants of the contaminated regions.
Timber and timber products are a viable economic resource.
Because of the high filtering characteristics of trees, deposition was often
higher in forests than in agricultural areas. When contaminated, the specific
ecological pathways in forests often result in enhanced retention of
contaminating radionuclides. The high organic content and stability of the forest
floor soil increases the soil-to-plant transfer of radionuclides with the result that
lichens, mosses and mushrooms often exhibit high concentrations of radio-
nuclides. The transfer of radionuclides to wild game in this environment could
pose an unacceptable exposure for some individuals heavily dependent on game
as a food source. This became evident in Scandinavia where reindeer meat had
to be controlled. In other areas, mushrooms became severely contaminated with
radiocaesium.
In 1990, forest workers in Russia were estimated to have received a dose
up to three times higher than others living in the same area (IA94). In addition,
some forest-based industries, such as pulp production which often recycle
chemicals, have been shown to be a potential radiation protection problem due
to enhancement of radionuclides in liquors, sludges and ashes. However,
harvesting trees for pulp production may be a viable strategy for
decontaminating forests (Ho95).
Different strategies have been developed for combating forest
contamination. Some of the more effective include restriction of access and the
prevention of forest fires.
One particularly affected site, known as the “Red Forest” (Dz95), lies to
the South and West close to the site. This was a pine forest in which the trees
received doses up to 100 Gy, killing them all. An area of about 375 ha was
104
severely contaminated and in 1987 remedial measures were undertaken to
reduce the land contamination and prevent the dispersion of radionuclides
through forest fires. The top 10-15 cm of soil were removed and dead trees were
cut down. This waste was placed in trenches and covered with a layer of sand.
A total volume of about 100 000 m
3
was buried, reducing the soil contamination
by at least a factor of ten.
These measures, combined with other fire prevention strategies, have
significantly reduced the probability of dispersion of radionuclides by forest
fires (Ko90). The chemical treatment of soil to minimise radionuclide uptake in
plants may be a viable option and, as has been seen, the processing of
contaminated timber into less contaminated products can be effective, provided
that measures are taken to monitor the by-products.
Changes in forest management and use can also be effective in reducing
dose. Prohibition or restriction of food collection and control of hunting can
protect those who habitually consume large quantities. Dust suppression
measures, such as re-forestation and the sowing of grasses, have also been
undertaken on a wide scale to prevent the spread of existing soil contamination.
Water bodies
In an accident, radionuclides contaminate bodies of water not only
directly from deposition from the air and discharge as effluent, but also
indirectly by washout from the catchment basin. Radionuclides contaminating
large bodies of water are quickly redistributed and tend to accumulate in bottom
sediments, benthos, aquatic plants and fish. The main pathways of potential
human exposure may be directly through contamination of drinking-water, or
indirectly from the use of water for irrigation and the consumption of
contaminated fish. As contaminating radionuclides tend to disappear from water
quickly, it is only in the initial fallout phase and in the very late phase, when the
contamination washed out from the catchment area reaches drinking-water
supplies, that human exposure is likely. In the early phase of the Chernobyl
accident, the aquaeous component of the individual and collective doses from
water bodies was estimated not to exceed 1-2% of the total exposure (Li89).
The Chernobyl Cooling Pond was the most heavily contaminated water body in
the exclusion zone.
Radioactive contamination of the river ecosystems (see Chapter 2) was
noted soon after the accident when the total activity of water during April and
early May 1986 was 10 kBq/L in the river Pripyat, 5 kBq/L in the Uzh river and
4 kBq/L in the Dniepr. At this time, shortlived radionuclides such as
131
I were
105
the main contributors. As the river ecosystem drained into the Kiev, then the
Kanev and Kremenchug reservoirs, the contamination of water,sediments,
algae, molluscs and fish fell significantly.
In 1989, the content of
137
Cs in the water of the Kiev reservoir was
estimated to be 0.4 Bq/L, in the Kanev reservoir 0.2 Bq/L, and in the
Kremenchug reservoir 0.05 Bq/L. Similarly, the
137
Cs content of Bream fish fell
by a factor of 10 between the Kiev and Kanev reservoirs, and by a factor of two
between the Kanev and Kremenchug reservoirs to reach about 10 Bq/kg (Kr95).
In the last decade, contamination of the water system has not posed a public
health problem. However, monitoring will need to be continued to ensure that
washout from the catchment area which contains a large quantity of stored
radioactive waste will not contaminate drinking-water.
A hydrogeological study of groundwater contamination in the 30-km
exclusion zone (Vo95) has estimated that 90Sr is the most critical radionuclide,
which could contaminate drinking-water above acceptable limits in 10 to
100 years from now.
Outside the former Soviet Union, direct and indirect contamination of
lakes has caused and is still causing many problems, because the fish in the
lakes are contaminated above the levels accepted for sale in the open market. In
Sweden, for instance, about 14 000 lakes (i.e., about 15% of the Swedish total)
had fish with radiocaesium concentrations above 1 500 Bq/kg (the Swedish
guideline for selling lake fish) during 1987. The ecological half-life, which
depends on the kind of fish and types of lakes, ranges from a few years up to
some tens of years (Ha91).
In the countries of the European Union, the content of
137
Cs in drinking-
water has been regularly sampled and reveals levels at, or below, 0.1 Bq/L from
1987 to 1990 (EC94), which are of no health concern. The activity
concentration in the water decreased substantially in the years following the
accident due largely to the fixation of radiocaesium in the sediments.
Sixteen years later
Over sixteen years after the accident, exposures of populations are mainly
due to the consumption of agricultural food contaminated with
137
Cs. Production
is today based on the following criteria:
• The contamination of foodstuffs should be at a level not leading to
an average individual doses higher than 1 mSv per year.
106
• Production of these foodstuffs should not be more expensive in
either economical or social terms.
• Some large population groups may receive low doses from these
contaminated foodstuffs, but collective dose and excess risk should
be evaluated.
In the Ukraine, agriculture in most contaminated territories produces
foodstuffs respecting the limits fixed the 25 June 1997: 100 Bq/l for milk
products; 200 Bq/kg for meat; 20 Bq/kg for potatoes and bread. Currently, milk
contamination levels are about 50 Bq/l.
However, there are large disparities in production in Ukraine, and some
private farms continue to produce milk more contaminated than the level fixed
by the new limits. This is due to animal grazing in contaminated meadows, and
to the large differences of transfer coefficients for caesium (1 to 20) depending
on the chemical composition of soils. Some experts predict that the fixation of
caesium in soils will be enough in the next 4 to 8 years to prevent more
contamination of foodstuffs, but some predictions seem more pessimistic.
(Sm00).
In Ukraine, 8,4 million hectares of agricultural soil are contaminated with
137
Cs, and are subject to countermeasures, mostly the use of fertilisers:
• The 54 900 hectares in the exclusion zone and the 35 600 ha
contaminated with more than 555 kBq/m2 are exclude from
agricultural farming.
• 130 800 ha are contaminated between 185 and 555 KBq/m2,
including 15 000 ha of peat bog where the transfer of caesium to
plants is the highest.
• 1.1 million ha contaminated between 37 and 185 kBq/m2, including
99 500 ha of peat bog.
• 7 238 millions ha contaminated between 3.7 and 37 kBq/m2.
An exclusion zone of about 4 000 km
2
has been defined, including a
circular area with a radius of 30 km around the reactor. The areas affected are
2 100 km
2
in Belarus, 2 040 km
2
in Ukraine and 170 km
2
in the Russian
Federation. All agricultural activities are forbidden, as is transfer of products.
However, studies are underway as to how the less contaminated portions of this
excluded land can be used.
Outside this area, 1.4 million of people are living on 30 000 km2 of land
contaminated higher than 185 kBq/m
2
, and 130 000 people are living in areas
107
where the contamination is higher than 555 kBq/m
2
. For the territories where
the annual dose is lower than 1mSv, life is considered as normal. When the
annual dose is higher than 1 mSv per year, people receive social compensations.
In Russia, some districts were declassified in January 1998, and this
decision was accepted badly by the affected populations.
The amount of agriculture products exceeding trade limits fixed by
Ukraine, Russia and Bielorussia are now very low, in spite of new restrictive
limits given by Ukraine in 1997 (100 Bq/kg for milk, 200 Bq/kg for meat,
20 Bq/kg for bread and potatoes). Today, the combination of soil transfers,
physical half-life of
137
Cs and efficacy of the countermeasures could lead to an
agricultural production that is lower than the fixed limits within the next 4 to
8 years. This means that, 20 to 25 years after the accident, food production
could be operated without any restriction.
In early 2001, 2 217 cities are still under radiological control in the
Ukraine. In fact, only 1 316 need permanent controls, but the population of the
901 remaining cities refuse the declassification of their areas because this could
be associated with the end of financial and social compensation.
In the exclusion zone, the impact on fauna and flora is characterised by
the extremely heterogenous deposition of radioactive particles, which produces
a wide range of doses to which the biota were subjected. In some cases, even in
very small geographic areas, the impacts differed by an order of magnitude
(IA01).
Somes consequences of the accident for the natural plant and animal
populations are determined by secondary ecological factors resulting from
changes in human activities. For example, the forbidding of hunting alters the
types and numbers of birds. In general, animal numbers have greatly increased
compared to adjacent inhabited areas. These favourable conditions for large
numbers of commercially hunted mammal species will be preserved (IA01).
The transfer of radionuclides by water and wind, and by extreme seasonal
weather conditions has not led to long term contamination beyond the exclusion
zone. In the exclusion zone, the future radioactive contamination will be
reduced slowly through radioactive decay.
The area in the exclusion zone covered by coniferous and deciduous
forests will increase to 65-70% of the whole zone. The areas of meadowland
and swap land will be correspondingly significantly reduced and gradually
replaced by forests. These changes create a stable and fire-resistant vegetation
108
layer. Associated with destruction of drainage systems, the level of groundwater
will rise (IA01).
Since the accident, trade of wood is regulated. Depending upon its use,
commercialisation levels range from 740 to 11 000 Bq of
137
Cs.kg
-1
. With this
new regulation, 30% of pines trees in the excluding zone are not usable.
In summary
• Many countermeasures to control the contamination of agricultural
products were applied with varying levels of efficiency. Never-
theless, within the former Soviet Union large areas of agricultural
land are still excluded from use, and are expected to continue to be
so for a long time. In a much larger area, although agricultural and
farm animal activities are carried out, the food produced is subject to
strict controls and restrictions on distribution and use.
• Similar problems, although of a much lower severity, were
experienced in some countries of Europe outside the former Soviet
Union, where agricultural and farm animal production were
subjected to controls and limitations for variable durations after the
accident. Most of these restrictions were lifted several years ago.
However, there are still some areas in Europe where restrictions on
slaughter and distribution of animals are applied. This concerns, for
example, several hundreds of thousands of sheep in the United
Kingdom and large numbers of sheep and reindeer in some Nordic
countries.
• Produce from forests, such as mushrooms, berries and game meat,
may continue to be a radiological protection problem for a long time.
The decrease of radioactivity will be now slow through radioactivity
decay.
• At present drinking water is not a problem. Contamination of
groundwater, especially with
90
Sr, could be a problem for the future
in the catchment basins downstream of the Chernobyl area.
• Contaminated fish from lakes may be a long-term problem in some
countries.
• However, the rehabilitation programmes must create conditions
attractive enough for a younger workforce, especially engineers and
qualified workers, to return. It is necessary and quite possible to
create conditions where the environmental contamination will not
result in the exclusion of important dietary components from
consumption.
109
Chapter VII
POTENTIAL RESIDUAL RISKS
The Sarcophagus
In the aftermath of the accident several designs to encase the damaged
reactor were examined (Ku95). The option which was chosen provided for the
construction of a massive structure in concrete and steel that used as a support
what remained of the walls of the reactor building (Ku95).
By August 1986 special sensors monitoring gamma radiation and other
parameters were installed in various points by using cranes and helicopters.
These sensors had primarily the function of assessing the radiation exposure in
the areas where the work for the construction was to be carried out.
An outer protective wall was then erected around the perimeter and other
walls in the turbine building, connected to the reactor Unit 3 building through
an intermediate building, the so-called “V” building, and a steel roof completed
the structure. The destroyed reactor was thus entombed in a 300 000 tonne
concrete and steel structure known as the “Envelope” or “Sarcophagus”. This
mammoth task was completed in only seven months, in November 1986.
Multiple sensors were placed to monitor such parameters as gamma
radiation and neutron flux, temperature, heat flux, as well as the concentrations
of hydrogen, carbon monoxide and water vapour in air. Other sensors monitor
the mechanical stability of the structure and the fuel mass so that any vibration
or shifts of major components can be detected. All these sensors are under
computer control. Systems designed to mitigate any changing adverse
conditions have also been put into place. These include the injection of
chemicals to prevent nuclear criticality excursions in the fuel and pumping to
remove excess water leaking into the Sarcophagus (To95).
An enormous effort was required to mount the clean-up operation;
decontaminating ground and buildings, enclosing the damaged reactor and
110
building the Sarcophagus was a formidable task, and it is impressive that so
much was achieved so quickly. At that time the emphasis was placed on
confinement as rapidly as possible. Consequently, a structure which would
effectively be permanent was not built and the Sarcophagus should rather be
seen as a provisional barrier pending the definition of a more radical solution
for the elimination of the destroyed reactor and the safe disposal of highly
radioactive materials. In these conditions, to maintain the existing structure for
the next several decades poses very significant engineering problems.
Consultations and studies by an international consortium are currently taking
place to provide a permanent solution to this problem.
The fuel in the damaged reactor exists in three forms, (a) as pellets of 2%
enriched uranium dioxide plus some fission products essentially unchanged
from the original forms in the fuel rods, (b) as hot particles of uranium dioxide a
few tens of microns in diameter or smaller particles of a few microns, made of
fuel fused with the metal cladding of the fuel rods, and (c) as three extensive
lava-like flows of fuel mixed with sand or concrete. The amount of dispersed
fuel in the form of dust is estimated to amount to several tons (Gl95).
The molten fuel mixture has solidified into a glass-like material
containing former fuel. The estimates of the quantity of this fuel are very
uncertain. It is this vitrified material that is largely responsible for the very high
dose rates in some areas (Se95a). Inside the reactor envelope, external exposure
is largely from
137
Cs, but the inhalation of fuel dust is also a hazard. As was
noted earlier, a small special group of scientists who have worked periodically
inside the Sarcophagus for a number of years have accumulated doses in the
estimated range of 0.5 to 13 Gy (Se95a). Due to the fact that these doses were
fractionated over a long time period, no deterministic effects have been noted in
these scientists. Since the beginning of 1987 the intensity of the gamma
radiation inside the structure fell by a factor 10. The temperature also fell
significantly. Outside the Sarcophagus, the radiation levels are not high, except
for the roof where dose rates up to 0.5 Gy/h have been measured after the
construction of the Sarcophagus. These radiation levels on the roof have now
decreased to less than 0.05 Gy/h.
Nine years after its erection, the Sarcophagus structure, although still
generally sound, raises concerns for its stability and long-term resistance and
represents a standing potential risk. Some supports for the enclosure are the
original Unit 4 building structures which may be in poor condition following
the explosions and fire, and their failure could cause the roof to collapse. This
situation is aggravated by the corrosion of internal metallic structures due to the
high humidity of the Sarcophagus atmosphere provoked by the penetration of
large quantities of rain water through the numerous cracks which were present
111
on the roof and were only recently repaired (La95). The existing structure is not
designed to withstand earthquakes or tornados. The upper concrete biological
shield of the reactor is lodged between walls, and may fall. There is
considerable uncertainty on the condition of the lower floor slab, which was
damaged by the penetration of molten material during the accident. It this slab
failed, it could result in the destruction of most of the building.
A number of potential situations have been considered which could lead
to breaches in the Sarcophagus and the release of radionuclides into the
environment. These include the collapse of the roof and internal structures, a
possible criticality event, and the long-term migration of radionuclides into
groundwater.
Currently, the envelope is not leaktight even if its degree of confinement
has been recently improved. Although the current emissions into the
environment are small, not exceeding 10 Gbq/y for
137
Cs and 0.1 GBq/y for
plutonium and other transuranic elements, disturbance of the current conditions
within the Sarcophagus, such as the dislodgement of the biological shield could
result in more significant dispersion of radionuclides (To95). The dispersion in
this case would not be severe and would be confined to the site provided that
the roof did not collapse. However, collapse of the roof, perhaps precipitated by
an earthquake, a tornado or a plane crash, combined with collapse of internal
unstable structures could lead to the release of the order of 0.1 PBq of fuel dust,
contaminating part of the 30-km exclusion zone (Be95).
More improbable worst case scenarios would result in higher
contamination of the exclusion zone, but no significant contamination is
expected beyond that area. Currently, criticality excursions are not thought to be
likely (IP95). Nevertheless, it is possible to theorise (Go95, Bv95) on
hypothetical accident scenarios, however remote, which could lead to a
criticality event. One such scenario would involve a plane crash or earthquake
with collapse of the Sarcophagus, combined with flooding. An accident of this
type could release about 0.4 PBq of old fuel dust and new fission products to
the atmosphere to contaminate the ground mainly in the 30-km zone.
Leakage from the Sarcophagus can also be a mechanism by which
radionuclides are released into the environment. There are currently over
3 000 m
3
of water in various rooms in the Sarcophagus (To95). Most of this has
entered through defects in the roof. Its activity, mainly
137
Cs, ranges from 0.4 to
40 MBq/L. Studies on the fuel containing masses indicate that they are not inert
and are changing in various ways. These changes include the pulverisation of
fuel particles, the surface breakdown of the lava-like material, the formation of
new uranium compounds, some of which are soluble on the surface, and the
112
leaching of radionuclides from the fuel containing masses. Studies to date
indicate that this migration may become more significant as time passes.
Another possible mechanism of dispersion of radioactivity into the
environment may be the transport of contamination by animals, particularly
birds and insects, which penetrate and dwell in the Sarcophagus (Pu92). Finally,
the possibility of leaching of radionuclides from the fuel masses by the water in
the enclosure and their migration into the groundwater has been considered.
This phenomenon, however, is expected to be very slow and it has been
estimated that, for example, it will take 45 to 90 years for certain radionuclides,
such as
90
Sr, to migrate undergound up to the Pripyat river catchment area. The
expected radiological significance of this phenomenon is not known with
certainty and a careful monitoring of the evolving situation of the groundwater
will need to be carried out for a long time.
Radioactive waste storage sites
The accident recovery and clean-up operations have resulted in the
production of very large quantities of radioactive wastes and contaminated
equipment. Some of these radioactive wastes are buried in trenches or in
containers isolated from the groundwater by clay or concrete screens within the
30-km zone (Vo95). A review of these engineered sites concluded that,
provided the clay layer remained intact, their contribution to groundwater
contamination would be negligible. On the other hand, 600 to 800 waste
trenches were hastily dug in the immediate vicinity of the Unit 4 in the
aftermath of the accident. These unlined trenches contain the radioactive fallout
that had accumulated on trees, grass, and in the ground to a depth of 10-15 cm
and which was bulldozed from over an area of roughly 8 km
2
. The estimated
activity amount is now of the order of 1 PBq, which is comparable to the total
inventory stored in specially constructed facilities next to Unit 4. Moreover, a
large number of contaminated equipment, engines and vehicles are also stored
in the open air.
The original clean-up activities are poorly documented, and much of the
information on the present status of the unlined trenches near Unit 4 and the
spread of radioelements has been obtained in a one-time survey. Some of the
findings of the study (Dz95) are that:
• The water table in the vicinity of Unit 4 has risen by 1 to 1.5 m in a
few years to about 4 m from the ground level and may still be rising
(apparently this is due mostly to the construction, in 1986, of a wall
3.5 km long and 35 m deep around the reactor to protect the Kiev
113
reservoir from possible spread of contamination through the
underground water, as well as to the ceasing of drainage activities
formerly connected with the construction of new units on the site).
• In the most targeted study area 32 of 43 explored trenches are
periodically or continually flooded.
• In that area the upper unconfined aquifer is contaminated every-
where with
90
Sr to levels exceeding 4 Bq/L. Caesium and plutonium
are less mobile and contamination from these elements is confined to
the immediate vicinity of the disposal trenches.
• The relative mobility of the
90
Sr is especially important in that, from
the closest trenches, it might reach the Pripyat River in 10 to
20 years.
It is clear that large uncertainties remain which require a correspondingly
large characterisation effort. For instance, at present, most disposal sites are
unexplored, and a few are uncharted; monitoring for groundwater movement is
insufficient and the interpretation of the hydrologic regime is complicated by
artificial factors (pumping, mitigative measures, etc.); the mechanisms of
radionuclide leaching from the variety of small buried particles are not well
understood, but are being studied.
Although it was previously felt that, radioelements could spread to the
Pripyat river and down stream to the Black see, this has not occurred.
Radionuclides have been effectively held up in soils and river sediments near
the accident site (see Chapter 2).
In summary
The sarcophagus was never intended to be a permanent solution to
entomb the stricken reactor. The result is that this temporary solution may well
be unstable in the long term. This means that there is the potential for collapse
which needs to be corrected by a permanent technical solution.
The accident recovery and clean-up operations have also resulted in the
production of very large quantities of radioactive wastes and contaminated
equipment which are currently stored in about 800 sites within and outside the
30-km exclusion zone around the reactor. These wastes are partly conserved in
containers and partly buried in trenches or stored in the open air.
114
In general, it has been assessed that the Sarcophagus and the proliferation
of waste storage sites in the area constitute a series of potential sources of
release of radioactivity that threatens the surrounding area. However, any
accidental releases from the sarcophagus are expected to be very small in
comparison with those from the Chernobyl accident in 1986 and their radio-
logical consequences would be limited to a relatively small area around the site.
As far as the radioactive wastes stored in the area around the site are concerned,
they are a potential source of contamination of the groundwater which will
require close monitoring until a safe disposal into an appropriate repository is
implemented. Radionuclides have not, however, migrated as far from the site as
was once expected.
Initiatives have been taken internationally, and are currently underway, to
study a technical solution leading to the elimination of these sources of residual
risk on the site. This will be developed in the following Chapter.
115
Chapter VIII
SHUTDOWN OF THE CHERNOBYL PLANT
1
The agreement to build the Chernobyl power plants dates from 1966,
when the former Soviet Union decided to develop nuclear production of
electricity. The RBMK reactor design also dates from this period. Six
1 000 MWe reactors were planned at that time.
Unit 1, which begin production in 1977, stopped in November 1996. In
December 1997, it was decided to decommission.
Unit 2, which was first connected to the grid in December 1978, was
stopped in 1991 after damage due to fire. The Ukrainian national authorities
decided to definitely close this plant in March 1999.
Unit 3, which started in 1981 has had many shut downs for maintenance,
inspections and repairs since 1997. In June 2000, the Ukrainian authorities
decided to close it definitely on 15 December 2000.
Units 5 and 6 were under constructions at the site at the time of accident,
but were never finished.
After the accident in reactor 4 and the fire in reactor 2, western countries
attempted to persuade the Ukrainian authorities to definitively close reactor
number 3. This was a priority for many countries in the bilateral exchanges and
agreements with Ukraine. This western pressure crystallised when the Ukrainian
parliament decided, in October 1993, to cancel a 1990s decision which
recommended to immediate stop of all RBMK reactor construction, and the
closure of the Chernobyl site. Later the European Union and the Ukraine
concluded, on 20 December 1995, a memorandum of understanding for the
closure of Chernobyl plant. In exchange for the definitive closure of all

1. This Chapter was prepared with the assistance of E. Gailliez and J.B. Chérié
(IPSN), (IP00, IP01).
116
Chernobyl plants, the European Union (in the framework of TACIS programme)
and western countries agreed to provide financial assistance to the Ukraine for
the provision of electricity, and to solve social problems resulting from the
closure of the site. Financial projects were estimated, in 1995, to be 2.3 billion
dollars. A part of these funds has been committed to modifications of reactor
number 3, creation of building for used fuel, and workshops for liquid and solid
waste treatments.
Later, many other projects relating to the modernisation of VVER
reactors have been discussed with the European Bank for Reconstruction and
Development (EBRD).
Concerning the stabilisation of reactor 4, the safety analyses for all
installations described in the next paragraphs will be jointly performed. From
the European side, the Riskaudit consortium, a common subsidiary of the
French IPSN (now the IRSN) and the German GRS in collaboration with
ANPA (Italy) and AVN (Belgium) under contract of the European Union will
perform this work. From the Ukrainian side, the Ukrainian State Scientific
Technical Center for nuclear and radiation safety (SSTC) will perform the work.
The two groups will combine their analyses for the benefit of the Ukrainian
Safety Authority (Nuclear Regulatory Department, NRD).
Preparation of the definitive dismantling of the Chernobyl power plant
It is planned to build different installations on the Chernobyl site to
accomplish the dismantling of the reactors. These facilities will be for the:
• storage of used fuel;
• treatment of liquids and solids wastes produced by dismantling
operations;
• storage of resulting waste packages.
Storage of used fuel
Used fuel coming from the three reactors is today stored inside reactor
cores, in pools close to the reactors, and in a former storage building. A new dry
storage installation is under construction, using the Nuhoms process, certified
by the US Nuclear Regulatory Commission. Two other building are under
construction. The first new building will be used for the cutting of fuel rods, and
117
the storage of control rods. The second building will consist to modular cells in
which containers including fuel will be inserted. Each cell will receive one
container. Cooling will be passive. It is planed to build 256 cells in 10 years.
Funding for this operation is provided through the EBRD, Westinghouse
(USA), Bouygues and Campenon Bernard (France), the operating western
companies for the Chernobyl Nuclear Power Plant operator.
This project began in June 1999, and buildings are under construction and
forecast receiving operating licenses in the beginning of 2003. Transfer of all
fuel assemblies is planned for the following ten years.
Treatment of liquids effluents
Liquid effluents, containing mainly
60
Co,
137
Cs,
134
Cs, are stored on the
site in two groups of tanks. The first group contains 5 outside tanks of 5 000 m
3
each, the second contains 9 tanks of 1 000 m
3
in individual cells. Today
26 000 m
3
are stored, the total capacity of the installation being 34 000 m
3
.
The treatment of these liquid wastes is a delicate operation, requiring the
construction of ventilated boxes for pumping operations. For the 5 000 m
3
tanks, it will be necessary to construct coverage.
Another building has been under construction since 2000, and will be
used for the transformation of these liquid wastes into solid wastes. Licensing of
this facility is planned for completion by the end of 2002. Transformation
operations will consist of mixing liquid wastes with concrete. The resulting
solid packages will be stored in a surface storage center close to Chernobyl. All
effluents produced by dismantling operations would be treated in these
installations. Liquid effluent processing operations are planned to last for ten
years.
These buildings are funded by the EBRD, Westinghouse (USA),
Belgatom (Belgium), SGN (France) and Ansaldo (Italy).
Treatment of solid wastes
A new installation for solid waste treatment is needed. Low and
intermediate-level wastes were generated by reactor operations, and consist of
metal, concrete, plastic, wood and paper. Today, these solid wastes are stored in
a decrepit building consisting in three compartments, the two first of which
(1 000 m
3
each) are quite full. The third compartment (1 800 m
3
), containing the
118
most highly contaminated wastes, is 20% filled, bring the total volume of waste
in this facility to approximately 2 350 m
3
. Currently, these wastes are covered
with concrete which must be removed and itself conditioned for disposal. This
existing storage installation can be used for waste conditioning, but only at a
rate of 3 m
3
per day.
The solid wastes produced during dismantling of the reactors will also
need to be treated. Wastes will be sorted, and low and intermediate-level wastes
will be stored in the surface storage site, outside the exclusion area of
Chernobyl site.
The most highly contaminated wastes will be inserted into waterproof
containers for temporary storage before future treatment. The workshop to
perform this waste conditioning will be built for a daily production of 20 m
3
.
These operations will be funded by European Union under the framework
of the TACIS programme. A call for proposals is in progress. The choice of the
western contractors will be decided for starting of operations at the end of 2003,
beginning of 2004. These operations are planned to last for at least 5 years.
The Sarcophagus
In the aftermath of the accident several designs to encase the damaged
reactor were examined. The Sarcophagus, build in only few weeks after the
accident, is largely described in Chapter VII, along with the potential residual
risks that the sarcophagus currently poses. Today, work is needed to reinforce
the existing sarcophagus to prevent or to limit radioactive dust releases, and to
reduce the risk of collapse either spontaneously of due to natural catastrophe. A
list of about 15 tasks has been established on the basis of estimated risks.
Today, only priority tasks have been performed, including the reinforcement of
a common ventilation chimney for reactors 3 and 4, and the reinforcement of
the roof concrete girders.
A new project, SIP (Shelter Implementation Plan) was launched in 1998,
to last for 8 years, by a working group of nuclear safety experts coming from
the G7
2
countries and the Ukraine. This project is funded by the EBRD, and its
cost is estimated to be 760 million dollars, 50 million of which will be paid by
the Ukrainian government.

2. The G7 group consists of the 7 more industrialized countries of the world; Canada,
France, Germany, Italy, Japan, United Kingdom and United States.
119
The SIP project has two main objectives; reinforcement of the
sarcophagus and enhancement of protection of workers and environment. Five
subsidiary objectives have been defined:
• reduction of the probability of sarcophagus collapse;
• reduction of consequence of an eventual collapse;
• increase of safety of the installation (criticality, management of
contaminated water, characterisation of materials containing
remaining fuel);
• increase of security of workers and environment;
• definition of a long tem strategy for safety.
This project is performed by a group independent from the Chernobyl
plant operator, and is assisted by a project management team unit including
Betchel and Battelle from USA, and EDF from France. This organization has to
main tasks: to define the elementary tasks for reaching SIP objectives, and to
request approval from competent Nuclear Regulatory Department of Ukraine.
Once more, the Ukrainian NRD will be assisted by the SSTC and western
companies (Scientech and Riskaudit).
Reinforcement of roof girders had involved about 300 workers. The
collective dose estimated from Ukrainian information is 3.5 man Sv, 10% for
preparation and 90% for the actual work. Preparative works had involved about
100 people, the highest doses were lower than 15 mSv, and approximately ten
people have received doses ranging from 10 to 15 mSv. The reinforcement
work has involved about 200 people, about 20 of whom have received doses
ranging from 30 to 40 mSv.
Ukrainian authorities claim that no workers have exceeded fixed the limit
for these operations, i.e. 40 mSv. The collective dose objective for the fifteen
tasks planed in the SIP project is 25 man Sv. Particular attention is being paid to
the monitoring of worker internal contamination.
Sarcophagus database
In the framework of “German-French initiative”, the IRSN (France) and
the GRS (Germany) have collaborated with the operator (CHNPP), the
International Scientific and Technical Center (ISTC) of the Ukrainian Academy
120
of Sciences, the Ukrainian National Engineering and Sciences Institute (NIISK),
and the Kurchatov Institute (Moscow) to produce a database on the “health
status” of the sarcophagus.
This database will facilitate and improve estimation of radiological risks
inside and outside the damaged building, and validate the today’s radiological
protection guidelines. This database will be used by SIP projects operators.
When finished this database will allow workers and planners to take a virtual
visit of the sarcophagus and its immediate surroundings. This database is based
on:
• construction and equipment of the sarcophagus, and new infra-
structure annexes;
• the radiological situation inside the sarcophagus (Kurchatov
Institute);
• the radiological situation in the vicinity of the sarcophagus (ISTC);
• gathering of data concerning amounts, quality, and characteristics of
radioactive materials inside the sarcophagus (Kurtchatov Institute).
The first version of this database was transmitted to the Chernobyl Center
in June 1999.
The social consequences
A large part of the 7 000 Chernobyl workers are living in Slavoutich city,
50 km east of Chernobyl. Ending the operation of the Chernobyl power plants
will reduce manpower needs on the site by about 2 000 people.
The closure of the Chernobyl site will be an additional stress on this region,
which has already suffered extensively as a result of the accident. The social,
economic and personal effects that the loss of employment at the site will have
on these individuals, these cities and this region should be studied and taken
into account in any final resolution of this situation.
121
Chapter IX
LESSONS LEARNED*
The accident did not affect each country in the same way and a different
emphasis was placed on various aspects of the accident with particular reference
to the circumstances of that country. Thus, countries remote from the accident,
with no domestic nuclear power programmes or neighbouring reactors, tended
to emphasise food control and information exchange as their major thrust for
improvement. Whereas those countries which were contaminated by the
accident, and had their own nuclear power programmes and/or reactors in
neighbouring countries, drew extensive lessons from the way the accident
developed and was treated. For these reasons, not all the lessons learned were
applied universally with the same emphasis.
Operational aspects
The Chernobyl accident was one of a kind, and, although it highlighted
deficiencies in emergency preparedness and radiation protection, it should not
be seen as the reference accident for future emergency planning purposes
(Bu91).
It was very clear from the initial reactions of the competent national
authorities that they were unprepared for an accident of such magnitude and
they had to make decisions, as the accident evolved, on criteria that could have
been established beforehand. This also meant that too many organisations were
involved in the decision making, as no clear-cut demarcations had been agreed
and established. Areas of overlapping responsibility and jurisdiction needed to
be clearly established prior to any accident. A permanent infrastructure needed
also to be in place and maintained for any efficient implementation of protective
measures. Such an infrastructure had to include rapid communications systems,
intervention teams and monitoring networks. Mobile ground monitoring teams

* With the contribution of Stefan Mundigl (OECD/NEA).
122
were required, as was aerial monitoring and tracking of the plume. Many
countries responded to this need by establishing such monitoring networks and
reorganising their emergency response.
Logistic problems associated with intervention plans, such as stable
iodine distribution (Sc94, NE95a) and evacuation obviously needed to be in
place and rehearsed long before the accident, as they are too complex and time-
consuming to be implemented during the short time available during the
evolution of the accident. Intervention actions and the levels at which they
should be introduced needed to be agreed, preferably internationally, and
incorporated into the emergency plans so that they could be immediately and
efficiently implemented.
The accident also demonstrated the need to include the possibility of
transboundary implications in the emergency plans, as it had been shown that
the radionuclide release would be elevated and the dispersion of contamination
more widespread. The concern, raised by the experience of Chernobyl, that any
country could be affected not only by nuclear accidents occurring on its territory
but also by the consequences of accidents happening abroad, stimulated the
establishment of national emergency plans in several countries.
The transboundary nature of the contamination prompted the inter-
national organisations to promote international cooperation and com-
munication, to harmonise actions (NE88, IA94, IC90, IC92, NE93, NE89,
NE90, NE89b, WH88, WH87, IA89b, IA92, IA91a, IA89c, IA87a, IA94a,
EC89a, EC89b) and to develop international emergency exercises such as those
organised by the OECD/NEA in its INEX Programme (NE95). A major
accomplishment of the international community were the agreements reached
on early notification in the event of a radiological accident and on assistance in
radiological emergencies through international Conventions in the frame of the
IAEA and the EC (EC87, IA86b, IA86c). In 1987, two Conventions came into
effect, namely the Convention on Early Notification of a Nuclear Accident
(“Early Notification Convention”) and the Convention on Assistance in the
Case of a Nuclear or Radiological Emergency (“Assistance Convention”). At
present, 83 States are Party to the Early Notification Convention, and 79 States
Parties to the Assistance Convention. In addition, the Food and Agriculture
Organisation of the United Nations (FAO), the World Meteorological
Organisation (WMO) and the World Health Organisation (WHO) are parties to
both conventions.
Based on these two conventions, the International Atomic Energy
Agency (IAEA) established a system for notification and information exchange
123
in case of a nuclear or radiological emergency, as well as a network to provide
assistance, on request, to affected countries.
The Council Decision 87/600/EURATOM of 14 December 1987
stipulated the European Community arrangements for the early exchange of
information in the event of a radiological emergency. Based on this council
decision, the European Commission established the European Community
Urgent Radiological Information System (ECURIE) through which the EU
Member States are required to notify the Commission on radiological
emergencies and to promptly provide available information relevant to
minimising the foreseen radiological information. The system focuses on
communication and information and data exchange in case of a nuclear or
radiological emergency.
Furthermore, in order to facilitate communication with the public on the
severity of nuclear accidents, the International Nuclear Event Scale INES was
developed by the IAEA and the NEA and is currently adopted by a large umber
of countries.
The accident provided the stimulus for international agreement on food
contamination moving in trade, promoted by the WHO/FAO, as there is a need
to import at least some food in most countries, and governments recognised the
need to assure their citizens that the food that they eat is safe. Monitoring
imported food was one of the first control measures instituted and continues to
be performed (FA91, EC89c, EC93a).
This event also clearly showed that all national governments, even those
without nuclear power programmes, needed to develop emergency plans to
address the problem of transboundary dispersion of radionuclides. Of necessity
these plans had to be international in nature, involving the free and rapid
exchange of information between countries.
It is essential that emergency plans are flexible. It would be foolish to
plan for another accident similar to Chernobyl without any flexibility, as the
only fact that one can be sure of is that the next severe accident will be
different. Emergency planners need to distil the general principles applicable to
various accidents and incorporate these into a generic plan.
The accident emphasised the need for public information and public
pressure at the time clearly demonstrated this need. A large number of persons
who are knowledgeable about techniques in providing information are needed to
establish a credible source of information to the public before an accident, so
124
that clear and simple reports can be disseminated continuously in a timely and
accurate form (EC89).
Emergency plans also need to include a process by which large numbers
of people could have their exposure assessed, and those with high exposures
differentiated. The accident also highlighted the need for the prior identification
of central specialised medical facilities with adequate transportation to treat the
more highly exposed individuals.
Refinement and clarification of international advice was needed (Pa88).
The recommendations for intervention in an accident contained in ICRP
Publication 40 were not clearly understood when they came to be applied, and
the Commission reviewed this advice in Publication 63 (IC92). This guide
placed emphasis on the averted dose as the parameter against which an
intervention measure should be assessed. It was also made clear that an
intervention had to be “justified” in as far as it produced more good than harm,
and that where a choice existed between different protection options,
“optimisation” was the mechanism to determine the choice. Emphasis was also
placed on the need to integrate all protective actions in an emergency plan, and
not to assess each one in isolation, as one may well influence the efficacy of
another.
Scientific and technical aspects
Prior to the accident, it was felt that the flora and fauna of the
environment were relatively radio-resistant and this was supported by the fact
that no lethal radioecological injuries were noted after the accident except in
pine forests (600 ha) and small areas of birch close to the reactor. A cumulative
dose of less than 5 Gy has no gross effect even in the most sensitive flora of
ecological systems, but there are still ecological lessons to be learned especially
on the siting of nuclear power reactors (Al93).
Plant foliar and root uptake is being studied, as are resuspension and
weathering. The transfer coefficients at all stages of the pathways to human
exposure are being refined. Following the accident, an assessment of the models
used at thirteen sites to predict the movement of
131
I and
137
Cs from the
atmosphere to food chains (Ho91) indicated that models commonly used tended
to overpredict by anything up to a factor of ten. The extensive whole-body
monitoring of radioactivity in persons undertaken in conjunction with the
measurement of ground and food contamination allowed refinement of the
accuracy of the models for human dose assessment from the exposure through
125
different pathways. The methods and techniques to handle contamination of
food, equipment and soil have been improved.
Meteorological aspects, such as the relationship between deposition and
precipitation and greater deposition over high ground and mountains, have been
shown to be important especially in the development of more realistic models
(NE96a). The importance of synoptic scale weather patterns used in predictions
was established, and different models have been developed to predict deposition
patterns under a wide variety of weather conditions. The chemico-physical
changes in the radioactive gases and aerosols transported through the
atmosphere are being studied to improve the accuracy of transport models.
Other impacts of the accident on model refinement include the
improvement in understanding the movement of radionuclides in soil and biota,
pathways and transfer factors; the effect of rainstorms and the influence of
mountains and the alignment of valleys on deposition patterns; particulate re-
suspension; long range pollution transport mechanisms; and the factors which
influence deposition velocities (NE89a, NE96).
Uniform methods and standards were developed for the measurement of
contaminating radionuclides in environmental samples.
In the case of high exposures, the importance of symptomatic and
prophylactic medical and nursing procedures, such as antibiotics, anti-fungal
and anti-viral agents, parenteral feeding, air sterilisation and barrier nursing was
demonstrated, as were the disappointing results of bone-marrow transplantation.
In addition, the accident led to an expansion of research in nuclear safety
and the management of severe nuclear accidents.
On the other hand, there is a need to set up sound epidemiological studies
to investigate potential health effects, both acute and chronic. In the Chernobyl
case, the lack of routinely collected data, such as reliable and complete cancer
registry data, led to difficulty in organising appropriate epidemiological
investigations in timely manner. There appears to be a need for developing and
maintaining a routine health surveillance system within and around nuclear
facilities.
In Russia, the government has decided to create a national system for the
handling of information on all aspects of crisis management. This system will
be operational at national level, but also at regional level. The database will be
managed by the IBRAE Russian Institute.
126
The INEX Programme (Nuclear Emergency Preparedness and
Management)
The OECD Nuclear Energy Agency (NEA), as a result of interest by its
member countries, has been actively involved in emergency planning,
preparedness and management for nuclear accidents, and created, in 1990, the
Expert Group on Emergency Exercises, which became later the standing NEA
Working Party on Nuclear Emergency Matters. This Working Party focuses on
innovative ideas and new approaches to improve existing procedures in place
for response to nuclear emergencies. In order to most efficiently achieve an
improvements, the group creates, as needed, temporary sub-groups with well
defined tasks, time lines and products, employing the most appropriate experts
from NEA Member countries, but also from non-NEA members. In addition,
the Working Party initiates the organisation of workshops and discussion
groups, the launching of questionnaires on specific topics, or the organisation of
international exercise series.
To explore, for the first time in an international context, the
transboundary aspects of nuclear accidents, the NEA initiated the preparation
and conduct of the first international nuclear emergency exercise INEX 1,
performed in 1993. With this table-top exercise, the international community
could for the first time test procedures and mechanisms in place to manage a
nuclear or radiological emergency, leading to a wealth of lessons learned and to
an improvement in nuclear emergency management. Three INEX 1 related
workshops allowed the exchange of experience in the implementation of short-
term countermeasures after a nuclear accident, in agricultural aspects of nuclear
and/or radiological emergency situations, and in nuclear emergency data
management.
The INEX 2 exercise series, also initiated by the NEA and performed
between 1996 and 1999, was more ambitious than the INEX 1 exercise, seeking
to improve actual emergency response procedures and existing “hardware”
through a truly international command post exercise. This experience
established for the first time an international nuclear emergency “exercise
culture” leading to a clear improvement of the international aspects of nuclear
emergency preparedness and management. The INEX 2 series offered a wealth
of lessons learned with respect to emergency planning and management,
particularly in the areas of communication and information exchange, public
and media information, and decision making based on limited and uncertain
information. The identified deficiencies in the area of communication and
information exchange led to the most prominent outcome of INEX 2 and a
major step forward in nuclear emergency management: the development of a
new communication and information exchange strategy Monitoring and Data
127
Management Strategies for Nuclear Emergencies, which is currently
implemented by various NEA member countries as well as by the international
community.
Regarding the role of international organisations, the INEX 2 series
contributed to better understanding who are the relevant international
organisations, what obligations and responsibilities each has, and how to co-
ordinate and harmonise their response in case of a nuclear emergency. The
relevant international organisations used the experience to establish a
mechanism for co-operation and collaboration through an Inter-Agency
Committee on the Response to Nuclear Accidents (IACRNA), for which the
IAEA serves as Secretariat.
On a national level, many countries participating in INEX 1 and INEX 2
exercises used the experiences and lessons learned to modify and improve
national procedures for nuclear emergency preparedness and management.
Countries also used the outcome of the exercises to update bilateral agreements.
In 2001, the INEX 2000 exercise was organised, similar to the four
INEX 2 exercises, as a command-post real-time notification and communication
exercise, dealing with the first hours of a nuclear emergency. In addition, the
INEX 2000 exercise included for the first time a second major objective, to test
compensation and third party liability issues after a nuclear accident, performed
as a NEA workshop in November 2001 focusing on decision-making
mechanisms in later phases of a nuclear emergency. This exercise, therefore,
served as a bridging exercise between the INEX 2 series and the next generation
of international nuclear emergency exercise programmes. On one hand, early
notification and communication exercises will be institutionalised by the IAEA
in collaboration and co-operation with other international organisations, and
repeated periodically. On the other hand, a new innovative INEX 3 programme
was initiated by the NEA to investigate post-accident management of
contaminated sites and regions.
In summary, the Chernobyl accident triggered the start of many national
and international programmes, which led to a considerable improvement of
national and international procedures for nuclear emergency management and
preparedness, especially in the areas of international communication and
information exchange, and in harmonisation of response. However, there still
remains room for improvement, for example in the field of co-ordinating and
harmonising the response to nuclear accidents, as well as in the area of decision
making in later phases after an accident. The work programmes of various
international organisations are focusing on these aspects.
128
Psycho-sociological programmes
ETHOS project
ETHOS is a European project that is looking at new methodologies for
sustainable rehabilitation of living conditions for inhabitants of contaminated
areas. It is a new approach to strategic co-expertise, and includes experts from
different fields of activities. The project also vigorously involves the local
population in the evaluation and the management of risk, in collaboration with
the local authorities and experts, (Lo99, He99) thus helping to restore their
confidence in experts and authorities.
The ETHOS methodology and practical approach were used in the first
stage (1996-1999), in the village of Olmany, which is located in the Stolyn
district of Belarus. This village, in the south east portion of Belarus, is located
200 km from Chernobyl. Great improvement in living conditions, especially in
the area of radiological protection and private farm production, was achieved
thanks to the strong involvement of the village people. A group of mothers
became involved in activities to improve the radiological protection of their
children. New pedagogic modules from this radiological protection culture were
later introduced in the village school.
While it is too early to draw final conclusions about the long term impact
of the actions implemented, it is interesting to note that during the project’s
three years, a profound change with regard to radiological protection took place
and several lessons have been learned. The first concerns the negative role
played by regulatory limits when they are interpreted as a boundary between
safe and unsafe. This was seen as a strong blocking factor, discouraging those
confronted by higher levels, and destroying any potential initiative an ALARA
attitude. The process followed by the mothers illustrates how it is possible to
develop a framework for setting protection targets, where limits lose their
previous status and are considered merely as a point of reference to guide
action.
On a village scale, the ETHOS project also has been successful at
improving the radiological quality of the food produced by the villagers. This
has improved the local economic and radiological situations in a “hand-in-hand”
fashion. The Bielorussian authorities, in agreement with European Union,
launched in 1999 a similar project at a district scale, the Stolyn district
(90 500 inhabitants). The aim of this second stage is to demonstrate that the
ETHOS process could be implemented in everyday activity by locals such as
physicians, nurses, head of collective farms, teachers and a radioactivity
129
measurement specialist to improve radiological and economic conditions. All
these activities are based on voluntary service.
Other studies
Murphy and Allen (Mu99) have studied the factors that determine
personal parameters guiding individuals to respect, or not, regulations regarding
forest used and forest product consumption. The gathering of mushrooms and
berries is, for these populations, a tradition and also a social and leisure activity.
Behavioural compliance, with forest and forest food restrictions, was largely
predicted by factors relating to behaviour itself: lifestyle factors. Factors
concerning radiation had little or no impact. This suggests that people’s
decisions about whether or not to go to the forest and consume forest produce
are largely based on whether they want or need to, and whether other people
they know are engaging in the behaviour. Concerns over radiation appear to
play little part in these behaviours.
However, more than sixteen years after the accident, these populations
that did not respect the measures of protection are not ignoring the radiation
situation, they are still aware of and concerned about the threat of radiation to
their health. This concern may manifest itself in the increased risk of stress-
related health problems.
In another study, Mays et al. (Ma99) have shown through the
consumption of contaminated milk in rural settlements that it is necessary for
the radiation protection experts to widen consideration of risk and impacts,
beyond radioactive dose, to social and psychological costs of both the nuclear
accident and countermeasures programmes.
In conclusion these studies clearly show the necessity to take in account
the socio-psychological factors for acceptance by the public of the radiological
protection measures taken by the national authorities.
In summary
Besides providing new impetus to nuclear safety research, especially on
the management of severe nuclear accidents, the Chernobyl accident stimulated
national authorities and experts to a radical review of their understanding of,
and attitude to radiation protection and nuclear emergency issues.
130
This led to an expansion of knowledge of radiation effects and their
treatment, and to a revitalisation of radioecological research and monitoring
programmes, emergency procedures, and criteria and methods for the
information of the public.
Moreover, a substantial role in these improvements was played by
multiple international co-operation initiatives, including revision and ratio-
nalisation of radiation protection criteria for the management of accident
consequences, as well as reinforcement or creation of international
communication and assistance mechanisms to cope with the transboundary
implications of potential nuclear accidents.
More than sixteen years after the accident, we can observe that its
consequences have not been completely addressed. Some pathologies have
appeared, the amplitude of these being not directly correlated with the real
impact of the accident.
But, one of the more spectacular lesson learned after the Chernobyl
accident is probably the change of government attitudes with regard to
technological catastrophes. The change includes the recognition of the need for
some common action at the international level, the admittance that a large
accident is possible, and the necessity to organize national and transboundary
exercises. In this field we can note the major role played by the NEA/CRPPH in
the INEX exercises, and the significant maturing of mentalities. This can be
measured by the fact that it was necessary to create artificial countries (Acciland
and Neighbourland) in the INEX 1 exercise, whereas subsequent exercises have
used real plants in real countries. These exercises are well appreciated by
national and local authorities, who do not hesitate to invite local media for
celebration of these exercises.
This important effort is now materialized in the form of an international
document, the Joint radiation emergency management plan of the international
organizations, jointly sponsored by Food and Agriculture Organization of the
United Nations, International Atomic Energy Agency, Nuclear Energy Agency
of the Organisation for Economic Co-operation and Development, United
Nations Office for the Co-ordination of Humanitarian affairs, World Health
Organization and the World Meteorological Organization (IA00).
131
EXPLANATION OF TERMS
Activity
Quantity of a radionuclide. It describes the rate at which spontaneous
nuclear transformations (i.e., radioactive decay) occur in it. It is measured in
becquerels (Bq), where 1 Bq equals one nuclear transformation per second.
Several multiples of the becquerel (Bq) are used throughout the text.
They are the following:
exabecquerel (EBq) = 10
18
Bq
petabecquerel (PBq) = 10
15
Bq
terabecquerel (TBq) = 10
12
Bq
gigabecquerel (GBq) = 10
9
Bq
megabecquerel (MBq) = 10
6
Bq
kilobecquerel (kBq) = 103 Bq
Collective dose
Total dose over a population group exposed to a given source. It is
represented by the product of the average dose to the individuals in the group by
the number of persons comprising the group. It is measured in person-sieverts
(person-Sv).
Dose
A general term denoting a quantity of radiation. Depending on its
application it can be qualified as “absorbed dose”, “equivalent dose” and
“effective dose”.
132
Absorbed dose
Quantity of energy imparted by radiation to a unit mass of matter such as
tissue. Absorbed dose is measured in grays (Gy), where 1 Gy equals 1 joule of
energy absorbed per kilogramme of matter. One gray produces a different
intensity of biological effects on tissue depending on the type of radiation
(alpha, beta, gamma, neutrons). One common submultiple of the gray, the
milligray, is often used. One milligray (mGy) is equal to 10-3 Gy.
Effective dose
Weighted sum of the “equivalent doses” to the various organs and tissues
multiplied by weighting factors reflecting the differing sensitivities of organs
and tissues to radiation. The weighting factor for each organ or tissue expresses
the fractional contribution of the risk of death or serious genetic defect from
irradiation of that organ or tissue to the total risk from uniform irradiation of the
whole body. Effective dose is measured in sieverts (Sv). Some submultiples of
the sievert are used throughout the text. They are the following:
millisievert (mSv) = 10-3 Sv
microsievert (µSv) = 10-6 Sv
Equivalent dose
Quantity obtained by multiplying the “absorbed dose” in an organ (e.g.,
thyroid) or tissue by a factor representing the different effectiveness of the
various types of radiation in causing harm to the organ or tissue. This factor,
whose value varies between 1 and 20 depending on the type of radiation, has
been introduced in order to allow grouping or comparing biological effects due
to different radiations. Equivalent dose is measured in sieverts (Sv). One sievert
produces the same biological effect, irrespective of the type of radiation.
Health effects
Acute radiation syndrome
A clinical scenario characterized by a complex of acute deterministic
effects affecting various organs and body functions in the irradiated person.
133
Deterministic effects (also called acute health effects)
Early deleterious radiation effects on living tissues (e.g., body, organ or
tissue death, cataracts), which generally occur only above a threshold of dose
and whose severity depends on the level of dose absorbed. They become
generally evident within a short time from the irradiation (hours, days or weeks,
depending on the dose received). Throughout the text the doses producing
Deterministic effects are expressed in grays (Gy).
Genetic effects (also called hereditary effects)
Stochastic effect which occur in the progeny of the exposed person.
Stochastic effects (also called late health effects)
Late deleterious radiation effects (e.g., leukaemia, tumours) whose
severity is independent of dose and whose probability of occuring is assumed to
be proportional to the dose received. It is also assumed that there is no threshold
dose below which stochastic effects will not occur. The stochastic effects occur,
therefore, at doses lower than those producing deterministic effects and may
manifest themselves after a long time (years, decades) from the irradiation.
Throughout the text the doses producing stochastic effects are expressed in
sieverts (Sv).
Intervention level
The value of a quantity (dose, activity concentration) which, if exceeded
or predicted to be exceeded in case of an accident, may require the application
of a given protective action.
135
LIST OF ACRONYMS
AUDR Soviet All-Union Dose Registry
CRPPH NEA Committee on Radiation Protection and Public Health
DNA Desoxyribonucleic Acid
EC European Commission
ECCS Emergency Core Cooling System
FAO Food and Agriculture Organization
GSF Forschungszentrum für Umwelt und Gesundheit
IAEA International Atomic Energy Agency
IARC International Agency for Research on Cancer
ICRP International Commission on Radiological Protection
INES International Nuclear Event Scale
INEX NEA Nuclear Emergency Exercises Programme
INSAG International Nuclear Safety Advisory Group
IPHECA International Programme on the Health Effects of the
Chernobyl Accident
IPSN Institut de Protection et de Sûreté Nucléaire
JAERI Japan Atomic Energy Research Institute
NAZ Nationale Alarmzentrale
NCRP Soviet National Committee on Radiation Protection
NEA OECD Nuclear Energy Agency
OECD Organisation for Economic Cooperation and Development
RNMDR Russian National Medical Dosimetry Registry
SKI Swedish Nuclear Power Inspectorate
UNSCEAR United Nations Scientific Committee on the Effects of Atomic
Radiation
WHO World Health Organization
137
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